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Bashford Dean Memorial Volume 



The number of occipitospinal roots in Chlamydoselachus, Heptanchus and Spinax 

 is unusually large. In Squalus (Text'figure 120) there are only two or three ventral 

 and two dorsal occipitospinal roots. These nerves united with the first and second 

 spinals are marked hh. in the figure. In Torpedo, a single (ventral) occipitospinal root 

 is present (Daniel, 1934). 



According to Daniel (1934), the occipitospinal nerves of Heptanchus innervate the 

 subspinaHs and dorsal interarcuales muscles; also, in elasmobranchs generally, the more 

 posterior of these nerves unite with the first group of spinal nerves to form the cervical 



Text-figure 120. 

 A projection, upon a sagittal plane, of the cranial, occipital and anterior spinal nerves of Squalus acanthias. 



hr.p., brachial plexus; hu.VII, buccalis of seventh nerve; d.X, ramus dorsalis of tenth; gn., first spinal gangUon; hh., hypobranchial 

 bundle; hmd., hyomandibularis; !!.X, lateral line nerve; md.e.VII, mandibularis externus of seventh; md.i.VII, mandibularis internus 

 of seventh; md.V, mandibularis of fifth; mx.V, maxillaris of fifth; op.V, ophthalmicus profundus; os.V, and os.VII, ophthalmicus 

 superficiaUs of fifth and seventh; ph.IX, pharyngeal branch of ninth; pi. VII, palatinus of seventh; po.t., post-trematicus of ninth; 

 pr.t., pretrematicus of ninth; sp., spiracle; st.IX, supratemporalis of ninth; st.X, supratemporalis of tenth; vi.X, visceral nerve; y and z, 

 occipitospinal nerves; II, optic; III, oculomotor; IV, trochlearis; VI, abducens; VIII, auditory nerve. 



From Daniel, 1934, Fig. 220; after Norris and Hughes, 1920, fig. 51 (in colors). 



plexus which in turn joins the pectoral plexus. The nerves of the cervical plexus separate 

 from the pectoral plexus and pass in front of the girdle to supply the hypobranchial 

 muscles, as in Scyllium and in Squatina (Fiirbringer, 1897). 



In her summary for the cranial nerves, Hawkes (1906) notes that the lower jaw of 

 Chlamydoselachus has been swung far back into a reptilian position, and suggests that 

 this may explain: (a) the absence of a typical maxillo-mandibular trunk; (b) the union of 

 branches of the vagus with one another and with the ramus lateralis vagi; and (c) the 

 great development of a hypoglossal musculature and the presence of a hypoglossal nerve. 

 She states that the number of roots by which the lateralis components arise confirms the 

 suggestion that, in origin, the acustico-lateralis components belong to a series of segments. 

 The connections between the acusticO'lateraHs elements of V, VII, and VIII show a ten' 



