DR. J. MUEIE ON THE ANATOMY OF THE SEA-LION. 



539 



leaving the innominata and common carotid, arches outwards, and at 1 J inch from these 

 sends off from the upper side its first branch, the vertebral, a vessel of considerable 

 thickness, almost equalling in this respect the common carotid. 



Fig. 3. 



Diagram of the arteries of the Base of the Brain. O.jubata. 



C. Internal carotid, severed close to posterior communi- 

 cating vessel. B. Basilar. Y. Vertebral cut short. 

 A M. Anterior median and a.sp. anterior spinal arteries. 

 a.c. Anterior cerebral, m.c. Middle cerebral, p.co. 

 Posterior communicating, p.e. Posterior cerebral, s.c. 

 superior cerebellar, a.i.c. Anterior inferior cerebellar, 

 and p.i.c. posterior inferior cerebellar arteries of left 

 side. t. Transverse branch. 



The vertebral artery proceeds but a short way forwards between the scalenus anticus 

 and longus colli muscles, then enters the foramen of the sixth, and continues within the 

 channel formed by the remaining cervical foramina situated at the roots of their trans- 

 verse processes. Emerging from the atloid vertebral foramen the artery winds round 

 the root of the superior articular process, and passes through a second foramen in the 

 atlas, which perforates the bone in front of the neural lamina ; thence it reaches the 

 interior of the spinal canal, to unite with its fellow of the opposite side. 



The left subclavian artery has a calibre as great as the trunk of the innominata. 

 It continues forwards and outwards towards the left, without branching, for 2 inches or 

 rather more; then the internal mammary shoots from its pectoral border. Three 

 quarters of an inch to the left of the internal mammary branch the subclavian trunk 

 divides into three. The largest vascular channel is the continuation of the subclavian 

 into the axillary. The upper smallest branch, but, moreover, relatively a large vessel, 

 is the left vertebral artery, which here, with a rather longer course in the neck than 

 the right vertebral, proceeds onwards to the skull as on the opposite side. The third 

 division is of intermediate size, and springs somewhat from above and behind the sub- 

 clavian trifurcation. It is equivalent to the thyroid axis, and through large transverse 



