478 Bashford Dean hiemorial Volume 



The innervation of the muscles that move the eyeball is shown (with the exception 

 of the abducens or sixth nerve, which innervates the external rectus) in my Figures 

 10, 11 and 12, plate IV. The chief peculiarities of the muscles (p. 392, Text'figures 66 and 

 67) are: (1) the external rectus is divided, as in some other elasmobranchs, into two 

 parts; and (2) all the recti muscles are attached to the top of the eyestalk, near its flat' 

 tened head. Allowing for these peculiarities of the muscles, the distribution of the third 

 (oculomotor), fourth (trochlear), and sixth (abducens) nerves is the same as in vertebrates 

 generally. The relations of these nerves are described by Allis (1923). 



Hawkes states that only one root of the trigeminal nerve (R.V. in Text'figure 

 119a and b) is recognizable macroscopically, though presumably both sensory and motor 

 components are present as in other forms. The single root is broad, but in a side view 

 it is almost completely hidden by the ganglion buccaHs {VII in Text-figure 119a and b). 



The ophthalmicus profundus nerve (Pro.), together with the ophthalmicus super- 

 ficialis V (S.Op.V.), originates from a small enlargement (presumably ganglionic) on the 

 inner side of the Gasserian ganglion {V in Text-figure 119b). Thus, as in Chimaera 

 (Cole, 1896) and in Petromyzon (Johnston, 1905.2), there is evidence that, at the present 

 time, the profundus (prf.) is a branch of the trigeminal, although in origin it belongs to 

 a more anterior segment (Johnston, 1905.1), as shown for Scyllium in Text-figure 117. 

 In both Chimaera and Petromyzon, the profundus nerve has an undoubted ganglion. 

 The distribution of this nerve is described by Hawkes (1906, p. 971) as follows: 



On entering the orbit the [profundus] nerve passes between the large rectus externus 

 muscle and the cranial wall, sending dorsally a long ciliary nerve which ends around the 

 upper part of the eyeball. The main nerve then passes outward, parallel with the oculomotor 

 nerve, to which it sends or from which it receives an anastomosing branch. Five mm. beyond 

 the origin of the ciliary branch the profundus passes somewhat ventrally between the eyeball 

 and the external rectus muscle to disappear in the eyeball, near the point of insertion of the 

 ventral part of the external rectus muscle. The profundus passes for about 1 cm. under the 

 covering membrane of the eyeball, emerging near the point where the optic nerve originates 

 from the eyeball. The nerve then passes anteriorly and out of the orbit immediately to the 

 outer side of the attachment of the inferior oblique muscle. Almost at once the nerve divides 

 into a number of branches, which spread over the olfactory capsules immediately below 

 the skin. 



The course of the profundus nerve in the region of the eyeball is illustrated in 

 Figures 10 and 12, plate IV, after Hawkes, who suggests that the anastomosis (A.B.) 

 between the profundus and the oculomotor nerve may comprise the fibers that connect 

 the ciliary ganglion and the oculomotor nerve, which here pass not directly to the ciliary 

 ganglion, but by way of the profundus. The distribution and relations of the profundus 

 nerve in the region of the eyeball are described in more detail by Allis (1923). 



Brohmer (1909) states that in his 25-mm. embryo of Chlamydoselachus the ciliary 

 ganglion occurs in the course of the nervus ophthalmicus profundus, which sends a branch 

 to the "nerve knot" on the wall of the premandibular cavity (Text-figure 118). From the 

 nerve knot a branch, which Brohmer calls the oculomotorius {Oc), extends forward. 



