BLOOD-VASCULAR SYSTEM OF THE LORICATI 59 
and 23a; C./’C.’A.’’), which passes between the ventral later- 
alis and the motor roots of the VII nerve to the roof of the 
skull, supplying the adipose tissue surrounding the brain and 
the semicircular canals. Emerging from beneath the motor 
root of the VII nerve, the auditory artery divides into an ante- 
rior and a posterior auditory artery. The anterzor auditory 
artery (Pl. Ill, figs. 23@ and 25; A.Aud.A.) follows along 
the anterior surface of the ramulus acusticus ampulle ante- 
rioris; passing beneath the anterior ampulla to which it gives 
off a branch, it continues on to the external ampulla and its 
semicircular canal. The posterzor auditory artery (Pl. III, 
figs. 23, 23@ and 25; P.Aud.A.), which at first passes caudad 
under the ramulus acusticus ampulle anterioris and the ramulus 
acusticus sacculi, comes up through the center of the latter and 
passes along in front of the ramulus acusticus ampulle poste- 
rioris, to supply the posterior ampulla, its semicircular canal, 
and the utriculus. The myelonal artery terminates in 2 forks 
on the ventral surface of the myel, in the region of the first 
spinal nerves. These branches usually anastomose with a 
branch of the first neural or vertebral arteries, which having 
their origin from the subclavians make them analogous to the 
anastomosis of the basilar and vertebral arteries of mammals, 
of which a more detailed description will be given under the 
subclavian arteries. At the point where the posterior cerebral 
artery bends to penetrate the mesencephalon it gives off, caudad, 
the cerebellum artery (Pl. Ill, figs. 23 and 24; Cer.A.). This 
vessel continues parallel, but above the IV nerve, ventrad to 
the optic lobes, and laterad to the crus. In its caudal course 
it gradually rises higher on the crus, until in the region of the 
posterior end of the optic lobes it gets to lie between the optic 
lobes and the valvula cerebelli. A little behind the origin of 
the IV nerve and the posterior end of the optic lobes this vessel 
penetrates the dorso-lateral wall of the valvula cerebelli at the 
point where the molecular layer of the valvula unites with the 
corresponding layer of the cerebellum. Its course is then 
caudad a little to one side of the median line, gradually ex- 
hausting itself in the granular layer of the cerebellum. 
The fourth and smallest vessel to be given off from the en- 
