THE LOWER VEUTEBRATA. 153 



they need not be further mentioned, v. also has the same 

 three branches, all emerging by a single aperture from the 

 skull, and with a similar distribution to those of the rabbit. 

 vii, differs in detail only from the rabbit's : the frog, not 

 being a biting or chewing animal, has a much smaller 

 amount of jaw- and face-muscle, so the branch which 

 is so greatly developed as to be counted the main facial 

 nerve in the rabbit, is here no larger than the others. It is 

 called the hyomandibular branch, and, originating anterior 

 to the internal ear, it curves back to run on the posterior 

 side of the tympano-Eustachian recess, on its way to the 

 jaw muscles. This part of its course in the rabbit is 

 obscured by the small size of the middle ear, and covered 

 in by the bulla : in the frog it is easily made out, but its 

 meaning will be better appreciated after we have studied 

 the dogfish. The other branches of vii. are the vidian or 

 palatine on the roof of the mouth, and a small pre-tympanic 

 that runs on the anterior side of the tympano-Eustachian 

 recess. Thus VII. is said to fork over this recess, which 

 separates two parallel branches of it. 



ix. and x. leave the skull behind the internal ear. ix. 

 sends a short branch to join the hyomandibular of vn. : 

 the rest of it goes to tongue and pharynx just as in the 

 rabbit, x. also has much the same distribution (see fig. 

 59, B.) as in the rabbit, when allowance is made for the 

 absence of a neck. It has no superior laryngeal branch 

 (although one has been inserted in the diagram for com- 

 parison), but has a recurrent laryngeal, and branches to 

 heart, lungs, stomach, and solar plexus. A small dorsal 

 branch of x. to the muscles at the posterior end of the 

 head may represent the rabbit's xi. ; otherwise it is wanting. 

 There is a hypoglossal nerve, but it is not xn., but the first 

 spinal. 



15. The Sympathetic System consists of a paired chain 

 of ganglia, one to each spinal nerve and united to it by a 

 ramus communicans. Posteriorly it is closely connected to 

 the median dorsal aorta : anteriorly, the right and left 

 halves diverge to follow the paired aortse, and so on to the 

 head where there are rami commiinicantes to x., ix., vjj.. 



