312 SPECIAL ANATOMY. 



heptangular circulus arteriosus Willisii, which lies over the sella tur- 

 cica, and surrounds the hypophysis cerebri. It is formed : the anterior 

 transverse wall by ramus communicans anter., the anterior, central, and 

 posterior lateral walls by Artt. cerebri anter., communicant, posterr., 

 cerebri profundce. 



556. 2. Art. thyreoidecB inferior, in the child larger, is sometimes want- 

 ing. Origin : close and next to art. vertebr., rather external (frequently in 

 common with supra- scapularis, as thyreo-cervicalis}. Course : first upwards 

 to the lateral border of the thyroid cartilage. Position : before the first curve, 

 carotis communis, ven. jugular, intern., n. Vagus, and sympathicus (ganglion 

 cervicale med.) ; before the second curve, nerv. recurrens ; behind it, art . 

 vertebral, andlongus colli ; oesophagus (to the left). Branches: to oesophagus, 

 trachea, m. scalenus antic., and longus colli. Farther: 



a. Cervicalis ascendens : ascends before scalen. antic., then between it and 

 rectus capit. antic, directly upwards to the basis cranii, gives rarni mus- 

 culares, and especially rr. spinales, which anastomose with the vertebralis. 

 With it is generally united : 



art. cervicalis superjicialis (into a common trunk ; thyreo-cervicalis'). 

 Course : transversely outwards through the fovea supraclavicul., to the 

 border of cucullar. Position: before scalen. antic. ,plex. brachial., levator 

 scapul.,&ndomo-hyoideus, one inch above the clavicle, higher than the 

 suprascapularis ; supplies cucull. scap., splenii, levator, &c. 



b. Laryngea inferior (s. thyreoidea superior, see before). 



c. Terminal branches, three; 1, at the inferior border; 2, at the sides of 

 the posterior surface of the thyroid gland ; 3, at the inferior border of 

 cartil. cricoidea. 



Art. thyreoidea infima (Neubauer) is not always present : arises from arcus 

 aortcs, carotis communis, or thyreoid. inferior ; passes before the trachea to 

 the gland. 



557. Superior external branches of the Subclavia. 



3. Scapularis posterior (s. transversa cervicis). Origin : generally outside 

 Scaleni (or inside, in common with thyreoidea infer. ; or between them, in 

 common with the suprascapular.). Course : transversely outwards through 

 plexus brachialis, curving backwards towards the superior posterior angle of 

 the scapula ; divides into : 



a. Cervicalis suprema ; ascends under the cucullar., ramifying in it, levator 

 scap., and splenius. 



b. Dorsalis scapulae winds under the levator and the angle of the scapula, 

 descends along the spinal border to the inferior angle between rhomboid. 

 and serratus post., and anastomoses with suprascap. and scapul. inferior. 



Situation : at first horizontally in the fossa supraclavicular., covered by 

 platysmamyoid., omohyoid., later by cucullaris and levator scapula;. 



4. Suprascapularis s. transversa scapulas. Or. : below art. thyreoid. inferior 



