IN THE PAEAGUAYAN LEPIDOSIREN, ETC. 349 



coramunicans occupies a slight groove on the exposed outer surface of the periotic 

 capsule at its junction with the proximal border of the suspensorium, and between the 

 dorsal extremity of the squamosal and the lateral margin of the fronto-parietal (fig. 1). 

 When viewed from the interior of the cranial cavity (PI. XXVIII. fig. 6) four foramina 

 may be seen in the cartilage of the periotic capsule, of which two are dorsally situated 

 and lie close together, just within the cavity of the capsule. The other two may be 

 seen on opposite sides of the utricular recess, near its anterior and posterior lips. The 

 dorsally-situated foramina (fig. 6, v.s.c.) are the extremities of the tubular canals in 

 which the anterior and posterior vertical semicircular canals are lodged, while each of 

 the remaining foramina (h.s.c.) transmits the ampullary end of a vertical canal and, in 

 addition, one extremity of the horizontal semicircular canal. 



The Glossopharyngeus (ix.).— From the cranial cavity the foramen for this nerve is 

 seen just within the hinder margin of the utricular recess (fig. 6, ix.). It perforates 

 the posterior portion of the periotic capsule and becomes visible externally just in front 

 of the aperture for the Vagus (PI. XXVIII. figs. 1 and 3, ix.). 



The Vagus (x.).— The foramen for this nerve is bounded anteriorly by the periotic 

 cartilage, and behind by an emargination in the anterior edge of the exoccipital bone 

 (PI. XXVIII. figs. 4 and 6, x.). The depression into which the cartilage opens 

 externally lodges the extraordinarily large Vagus ganglion (PI. XXVIII. fio- s . 1 

 and 3, x.). 



The Anterior Spinal Nerves.— As correctly described by Hyrtl (I c), the dorsal and 

 ventral roots of the first spinal nerve (Hypoglossal) emerge through a deep but narrow 

 notch in the hinder border of the exoccipital (PL XXVIII. figs. 1 and 4, sp.n.i), but 

 the roots of the second nerve, instead of traversing a foramen in the exoccipital as in 

 Protopterus, perforate the fibrous wall of the neural canal between that bone and the 

 first neural arch (figs. 1 and 4). The main trunks of the two nerves pass downward 

 and a little forward, and unite to form the brachial nerve externally to the proximal 

 third of the " cranial rib." 



Wiedersheim figures and describes in Protopterus (I. c. fig. 10) a branch of the Vagus 

 as fusing with the main trunk of the first spinal nerve (Hypoglossal), dorsad to the 

 junction of the latter with the second and third spinal nerves to form the brachial 

 nerve. The existence of this singular anastomosis has also been affirmed by Iversen 

 [19] and more recently by Newton Parker [ 33 ]. On the other hand, it is expressly 

 stated by Pinkus (I. c.) : « Vaguselemente habe ich in den Plexus brachialis nicht 

 iibertreten sehen, im Gegensatz zu den Angaben von Wiedersheim, Iversen, und Parker, 

 und in Uebereinstimmung mit dem Befund bei Lepidosiren paradom " (p. 331). 



With reference to Lepidosiren it may be stated that although the brachial nerve 

 contains no " Vaguselemente," yet a connection does undoubtedly exist between a 

 branch of the Vagus and the Hypoglossal. Near the point of junction of the Hypo- 

 glossal with the second spinal nerve to form the brachial nerve the former gives off a 



vol. xiv. — part v. No. 4.— February, 1898. 2 z 



