1888.] and Distribution of the Cranial Nerves. 389 





Muscles from myotomes 

 (somatic). 



Visceral 

 clefts. 



Muscles from lateral 

 plates 

 (splanchnic) . 



1st segment. . 

 2nd „ . . 

 3rd „ .. 

 4th „ 

 5th „ . . 



eth „ .. 



1 7th „ ] 

 8th „ \ 

 9th •„ J 



Eye muscles, Illrd nerve 

 IVth „ 

 Vlth „ J 



Muscles from skull to f 

 shoulder girdle Xllth < 

 nerve |_ 



1. Mandibul. 



2. Hyoid 



3. 1st branch. 



4. 2nd „ 



5. 3rd „ 



6. 4th „ 

 7 



Yth motor part"") ^ 



1 si °° 



? U 



X 



From which we see that if we look upon the myotomes as repre- 

 senting the primitive segmentation, while the visceral clefts and 

 muscles from the lateral plates of mesoblast represent the secondary 

 segmentation (Branchiomery), the 4th, 5th, and 6th segments are 

 unrepresented by any muscles, or rather the 4th and 5th, for he 

 notices the slight muscle formation in the 6th somite, but was unable 

 to trace any special muscle to it. 



Now looking at these two groups of muscles, the splanchnic and 

 somatic, we see that the muscles of mastication and expression differ 

 in structure, colour, nature of contraction, and general appearance 

 from the muscles of the eye and the somatic muscles generally, with 

 the exception of the specialised tongue muscles. I find also that the 

 motor nerves of the Illrd, IVth, and YIth nerves are in the dog much 

 larger in calibre than those of the facial and slightly larger than 

 those of the trigeminal, the eye muscles being innervated by nerves 

 of the same size as the large motor nerves of anterior roots, i.e., from 

 14"4 fi — 18 /ul, while the facial muscles are innervated by nerves of 

 the same size as the large motor nerves of the vagus and glosso- 

 pharyngeal which supply the pharyngeal and laryngeal muscles, 

 i.e., from 9 fi — 10*8 ft. 



Any nerve fibres, therefore, of the size of those of the Vlth 

 nerve, for instance, would be very conspicuous and easily followed if 

 they appeared in among the smaller fibres of the facial. Such is the 

 case ; the facial roots possess a group of large fibres of the size of the 

 somatic motor nerves in among the smaller fibres ; a series of sections 

 through the facial has enabled me to trace one group of these large 

 fibres, and it is a beautiful sight to see them separating out one by 

 one to come to the edge of the nerve, and finally to form a small 

 nerve, which is found to be the n. stapedius. The rest of them leave 

 the facial nearer its exit from the brain, and I think pass out as the 

 nerve supplying the Levator veli palati muscle. The difficulty, how- 

 ever, of combining the dissection of these parts with the necessary 



2 f 2 



