The Anatomy of Chlamydoselachus 481 



Hawkes finds many small branches of the maxillary nerve which terminate in the 

 mucosa of the roof of the mouth and are therefore visceral, but she thinks it probable 

 that these visceral components belong to the facial nerve and are only secondarily united 

 with the trigeminal. 



Every student of comparative anatomy is familiar with the difficulty of separating 

 the fifth and the seventh nerves where parts of different nerves are interwoven or run 

 in the same sheath. Hawkes (1906, pp. 968 and 969) states that in Chlamydoselachus: 



No complete union between the [fifth and seventh] nerves has been found, except for 

 a distance of about 1 cm. on the left side, where a branch of the ramus buccalis and of the ramus 

 maxillaris are inseparable. The appearance of union occurs chiefly in the region just beyond 

 the orbit, where there are plexiform connections between the buccalis VII, mandibularis V, 

 maxillaris V, and their branches. Here, when two or more nerves come into close contact, 

 they are loosely or tightly bound together by connective tissue, but, in all cases except the 

 one mentioned above, in such a way that a separation can be effected by careful dissection. 

 The smaller branches and these pseudo'unions vary considerably on the two sides of the 

 same specimen and in different specimens. The variabihty, which is met with in every 

 system of Chlamydoselachus, suggests that the species has considerable anatomical instability. 



There is considerable difference of opinion as to what parts, in the region of the 

 gangliated roots, belong to the fifth and seventh nerves respectively. In most elasmo' 

 branchs the ganglion of the buccal division of the seventh or facial nerve is intimately 

 associated with the Gasserian ganglion, and the two are often inseparable. In Chlamy^ 

 doselachus the two ganglia are distinct medially, as shown in Text'figure 119b, after 

 Hawkes. Concerning some interrelations of the fifth and seventh nerves AUis (1923, pp. 

 209 and 210) writes: 



The nervi profundus and trigeminus, as I interpret these nerves, arise by two main 

 roots, the anteroventral one of which is formed by the combined roots of the profundus 

 and that part of the trigeminus that is currently considered to form the entire nerve. The 

 other root arises by two rootlets, in close connection with the root of the nervus facialis, the 

 two rootlets being the facialis roots A and B of Merritt Hawkes' descriptions. This root 

 joins the anteroventral root inside the cranial cavity, and, in the specimen used for the 

 accompanying Fig. 58, the two roots traverse the membrane that forms the mesial wall of 

 the acustico'trigemino-faciahs recess through a single foramen which lies anterior to the 

 foramen for the root of the nervus facialis and wholly separate from it. In the acustico' 

 trigemino'facialis recess these two roots enter a ganglionic complex, but this complex was 

 not particularly examined. According to Merritt Hawkes a ganglion forms on each of the 

 two roots, one of which she calls the Gasserian ganglion and the other the buccalis ganglion, 

 the latter ganghon lying dorsal to the former and wholly [?] separate from it. On the "inner 

 side" of the Gasserian ganglion there is said to be a small sweUing, from which the rami 

 profundus and superficial ophthalmic V arise, side by side and of equal size. Comparison 

 of these conditions, as thus described, with those in Squalus acanthias and Mustelus califor- 

 nicus, as described by Norris and Hughes (1920), would seem to establish beyond question that 

 the anterior root of Chlamydoselachus is composed entirely of motor and general sensory 

 (spinal V) fibers, that the little swelling on the inner side of the so'called Gasserian ganglion 

 is the ganglion of the nervus profundus, and that the posterior root of the complex derives 



