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The basilar artery may exist as two longitudinal trunks that may be united by anastomoses. Occasionally, the basilar splits into two vessels that reunite. When the two vessels fuse, the resulting single vessel may have a median sagittal partition. In some subjects, the basilar passes through a foramen in the dorsum sellae. An aberrant branch may arise that pierces the dorsum sellae and joins the internal carotid.
The vaginal artery usually arises from the uterine artery, sometimes as several branches. It may also arise from the internal iliac in common with the uterine artery. The vaginal artery may also arise from the middle rectal or from the superior, or inferior vesical artery.
This artery may form a common trunk with the superior gluteal (Jaschtschinski, 25%; Lipshutz, 43%). It has been reported doubled and it may be joined to the obturator. The ischiadic (sciatic) artery, the embryonic axis artery, "arises" from the inferior gluteal artery. It may persist as the primary artery of the thigh and continue into the leg as the popliteal. The ischiadic (sciatic) artery (a. comitans n. ischiadic) is usually a long, thin vessel which is normally the arterial blood supply to the sciatic nerve.
Poynter considered this artery the most constant of the axillary branches. This artery may arise from the thoracoacromial (6% of Poynter's series of 200 cadavers). Occasionally, the subscapular arises from the second part of the axillary (15%), and it may also arise from the brachial. Quite often it arises from a common trunk with one or both circumflex humeral arteries (15%). It may arise as a branch from the lateral thoracic, posterior circumflex humeral, or profunda brachii. The posterior circumflex humeral artery may arise from, or form a common trunk (15%) with, the subscapular artery.
The deep brachial is the largest branch of the brachial although there is considerable variation in its origin. In 55% of individuals it arises as a single trunk from the posteromedial side of the brachial, slightly below the lower margin of the tendon of the teres major muscle.
The branches of the third part of the axillary artery are subject to great variation. The two circumflex arteries may arise from a common trunk (20% of individuals, Poynter; 6%, according to Quain; 22%, Pellegrini; 16%, Hitzrot), usually alone or rarely together with profunda brachii and muscular branches. In a study of 610 limbs, the anterior artery had a common origin with a neighboring vessel in 20.2% of cases, most frequently with the posterior artery (13.4%). It is usually small, is doubled in 8% of cases, and is the last branch of the axillary in 35% (Poynter).
This artery may be a branch of the vertebral, in which case it passes through the transverse foramen of the seventh cervical vertebra and between the ribs and transverse processes of the upper three intercostal spaces. The supreme intercostal may arise from the costocervical trunk, thyrocervical trunk, deep cervical (cervicalis profundus), inferior thyroid, second intercostal, or axillary. The left artery has been reported as a branch of the aortic arch in cases having four arch branches. In one case it arose from a lateral internal thoracic artery.
In 70% of individuals, this artery arises from the second or third part of the subclavian as an independent branch. In 30%, it arises from the transverse cervical artery. If this inconstant artery arises from the subclavian, it usually passes dorsally between the trunks of the brachial plexus (middle and superior in 46%, and middle and posterior in 44%). It may perforate the middle and posterior scalene muscles; these two muscles usually form a common mass.
This artery is sometimes poorly developed or even terminates as the stylomastoid artery. It may arise in common with the ascending pharyngeal (Livini, 1%) or with the occipital; the occipital may replace an absent posterior auricular. An infrequent branch is the transverse facial. When the posterior auricular is larger than usual it may be compensating for a deficiency in the occipital or the superficial temporal artery. Superficial Temporal
This artery often arises from the common carotid, with the facial and less frequently with the superior thyroid. The lingual, facial and superior thyroid may arise from a common trunk. It may also arise in common with the facial artery (Faller, 10-20%) or with the superior thyroid or both of these with the maxillary artery (Haller, 14%; Quain, 20%; Livini, 25%; Dall'Acqua, 20%; Poynter, 15%) or with the ascending pharyngeal (Livini, 0.5%). The lingual sometimes branches from the facial.
The transverse cervical artery arises from the subclavian in about 61% of cases and from the thyrocervical trunk in about 38%. When it arises from the subclavian, it is usually behind or lateral to scalenus anterior. When it is absent, it is compensated for by branches from the dorsal scapular, superficial cervical, costocervical trunk, or the distal or third part of the subclavian or even the axillary artery. If the artery arises medial to scalenus anterior it is, without exception, a branch of the thyrocervical trunk. It may arise from the dorsal scapular (possibly as high as 20%).
The occipital may be a branch of the internal carotid, thyrocervical trunk, inferior thyroid, or its ascending cervical branch. The posterior auricular (Livini,12%), ascending pharyngeal, or stylomastoid may be branches of the occipital. It sometimes arises in common with the ascending pharyngeal (Quain, 13%, Livini 16%), or is continuous with a vertebral artery through a large anastomosis. A major portion of the occipital artery may pass over the sternocleidomastoid muscle, with only a small artery being located in its usual position.
When this artery is absent it is replaced by branches from the superficial cervical, suprascapular, or vertebral artery. According to Röhlich the ascending cervical artery arose from the inferior thyroid artery as follows: Right side, 76 cases (79.1%); Left side, 68 cases (74.7%); total 144 cases (79.1%); in Men, 95 cases (77.2%); in Women, 53 cases (87.5%). The ascending cervical arose with the transverse cervical artery from a common stem. Right side, 3 cases (3.1%); left side, 5 cases (5.7%); total, 8 cases (4.3%); in Men, 6 cases (4.8%); in Women, 2 cases (3.1%).
A branch of the descending genicular artery, the last branch (most distal) of the femoral, the saphenous is also variable. It usually lies between the sartorius and the garcilis muscles and supplies their distal ends. The artery accompanies the saphenous nerve. It usually supplies the skin on the medial and proximal part of the leg. The artery may continue to join, in varying degrees, the dorsalis pedis artery and plantaris pedis arteries.
The internal pudendal artery may arise in common with the obturator or the umbilical. It may end as a perineal artery, with the artery to the penis arising from the internal iliac. In some cases, it splits into two vessels, one of which remains in the pelvis to supply pelvic viscera. The internal pudendal is necessarily, always a branch of the anterior division of the internal iliac artery. The dorsalis penis artery may arise from profunda femoris or femoral artery. The inferior rectal artery is typically a branch of the internal pudendal artery.
The internal iliac may be longer or shorter than usual. It is seldom less than 2.5 cm in length, but may be as short as 1.2 cm or as long as 7.5 cm. Length variation generally depends upon the length of the common iliacs; when they bifurcate higher than usual, the internal iliac is longer and may lie initally above the brim of the true pelvis. The length may also depend upon the internal iliac itself dividing higher or lower than usual into its usual branches. This division may occur anywhere between the pelvic brim and the upper border of the sacrosciatic foramen.
A significant median artery (comes nervi mediani) may persist in the adult (8%). The main supply of the hand in the embryo is the median artery. This is followed, in development, by the anterior interosseous, which is finally replaced by the ulnar and radial arteries as the principal blood supply of the hand. Either the the anterior interosseous or the median may enter into the formation of the superficial palmar arch if the ulnar is deficient or absent.
The posterior tibial may be absent (Quain, 1844), rudimentary, or replaced by the peroneal artery. It may supply all the common digital arteries. On occasion, it pierces the interosseous membrane to join the anterior tibial. It may turn anteriorly (in the distal quarter of the leg) to replace the anterior tibial. The peroneal in such cases provides the medial and lateral plantar arteries. The peroneal is sometime absent or enhanced by a branch from the posterior tibial. The great saphenous artery may arise from the posterior tibial artery.
The arch may be doubled or absent, in which case the plantar foot is supplied by a single vessel, the posterior tibial. See illustrations of arterial variations in the foot. There is obviously much variability in the dorsalis pedis artery and it is difficult to provide well-defined patterns for this artery. However, Dubreuil-Chambardel (see image 267, below. Series A) reported the following frequencies for each of his seven types: A. I - 18/165; A. II - 56/165; A. III + A. IV- 2/165; A. V- 2/165 ; A. VI - 14/165; A. VII - 46/165; A. VIII - 2/165.
Embryologists have shown us that the hand is vascularized as follows: the median artery develops the earliest, followed by the interosseous, and this vessel is finally (and usually) replaced by the ulnar and radial arteries. These changes during development permit a wide range of vascular variations to occur. The mature arch supplied by a comes nervi mediani (median artery) represents a persistence of the earliest embryonal blood supply of the hand. The superficial palmar arch is subject to significant variations. The completion of the arch on the radial side is extremely variable.