The Anatomy of Chlamydoselachus 483 



nent of the vagus, whereas, in all cases, so far as is known, the remains of that component 

 have passed [as ventral occipitospinal roots] into the hypoglossal. . . . This would indeed 

 be a primitive condition." Garman (1885.2) does not mention any occipitospinal nerves, 

 but the ventral roots labeled "10" in his Fig. A, pi. XVI (my Figure 26, plate VI) are 

 probably occipitospinales. 



Hawkes found, in Chlamydoselachus, four (pairs?) of spino-occipital (occipitospinal) 

 nerves, which pass out of the cranium by four separate foramina. Three of these roots 

 are shown in Figure 13, plate IV, after Hawkes. No ventral occipitospinal roots 

 are shown in Hawkes' figure of the ventral surface of the brain. She records that two of 

 the occipitospinal roots were placed completely under, the third partly under, the cover 

 of the vagal roots. Immediately outside the cranium the occipitospinal nerves unite into 

 a flattened strand, the hypoglossal nerve. Hawkes states that the third and fourth 

 occipitospinales of Chlamydoselachus have each a dorsal branch, which, like the dorsal 

 branches of the succeeding spinal nerves, passes upward and backward. No dorsal 

 branches were found on the first two occipitospinal nerves. 



Johnston (1905.1, p. 231) interprets the occipitospinal nerves as follows: ''The 

 dorsal and ventral 'hypoglossal' roots need not be considered as spinalartige nerves. 

 They probably are not equivalent to spinal nerves at all, but are only the general cutaneous 

 and somatic motor components of nerves of the vagus region, the visceral sensory and 

 motor components of which have been collected into a single large vagus root." 



In his 25'mm. embryo, Brohmer (1909) describes and figures (my Text-figure 118) 

 a series of ventral roots lying between the main branches of the vagus. The first of these 

 (l.u.) is present on only one side, and is very small; the others are paired. Brohmer 

 states that six of these ventral roots are occipitospinal nerves, but it seems possible 

 that only four or five of the most anterior ones are really occipitospinales, the remaining 

 posterior ones being ventral roots of spinal nerves. (Daniel, 1934, states that "as many 

 as five" of the ventral occipitospinales have been located on each side in the young of 

 Heptanchus and Chlamydoselachus). Dorsal to the third and fourth ventral roots, 

 Brohmer found two ganglionic masses (Ggl.I., Ggl.2.), which he interprets as remains 

 of the ganglionic crest. The more posterior of the two masses has two rootlets. 



In Heptanchus (Fiirbringer, 1897; Daniel, 1934) there are four pairs of ventral 

 occipitospinal nerves or roots (Text'figure 116, w-z), but only two pairs of dorsal roots 

 (Figure 28, plate VII). The members of the first dorsal pair join the corresponding 

 members of the third ventral pair to form a pair of nerve trunks resembling spinal nerves 

 in that they have both dorsal and ventral roots. The first roots to arise ventrally are 

 near the median line and in origin are not unlike the sixth or abducens nerves. 



In a 26'mm. embryo of Spinax described by Braus (1899) there were four pairs of 

 ventral roots representing occipitospinal nerves. Of these, one on the left and two on 

 the right were joined by dorsal roots bearing ganglia, thus increasing the resemblance 

 to spinal nerves. 



