IN THE PARAGUAYAN LEPIDOSIREN, ETC. 347 



Trigeminus (v.'). Externally, the nerve issues from the cranial cavity immediately 

 dorsad to the trabecular cartilage, and thence passes forward to the usual eye-muscles 

 (PL XXVIII. fig. 1, HI). 



The Trigeminus (v.). — The various divisions of the Fifth and Seventh cranial nerves 

 and certain of their principal branches are related to a considerable number of 

 diversely-situated cranial foramina. With the exception of the ramus ophthalmicus 

 of the Fifth nerve, their primary branches may almost be said to leave the cranial cavity 

 by a single large foramen leading into a lateral diverticulum of the cavity situated at 

 the junction of the trabecular and periotic cartilages, and bounded anteriorly by the 

 former and posteriorly by the latter cartilage. This diverticulum will in future be 

 referred to as the Gasserian recess. The separation and divergence of the primary 

 branches of these nerves lead to the formation of a number of closely-related foramina 

 of various sizes, either at the outer extremity of the recess or in its margins and floor. 



The first division of the Trigeminus, or the ramus ophthalmicus, leaves the cranial 

 cavity by a separate foramen in the hinder part of the trabecular cartilage, immediately 

 behind the junction of the parasphenoid and fronto-parietal bones (PI. XXVIII. 

 fig. 6, v.'), and, after a short course obliquely outward and forward, emerges on the 

 lateral surface of the skull a little dorsad to the first appearance of the trabecular 

 cartilage externally (PL XXVIII. fig. 1, v.'). From this point the nerve passes directly 

 forward parallel to the trabecular cartilage and dorsad to the eye. One branch of its 

 ramus ophthalmicus profundus traverses a foramen in the fibrous. tissue of the posterior 

 wall of the nasal capsule, situated immediately anterior to the root of the upper labial 

 cartilage (fig. 1), and then runs forward between the cartilaginous roof of the capsule 

 and the membranous wall of the enclosed olfactory sac ; eventually the nerve issues 

 from the nasal capsule through a minute foramen in the extreme anterior part of its 

 roof (PL XXVIII. figs. 2 and 5, v.'j?.), and is then joined by another branch of the 

 same nerve, which, in its course to the junction, has remained external to the nasal 

 roof and parallel to the outer margin of the dermal ethmoid. The ramus maxillaris 

 and the ramus mandibularis emerge through a single large foramen in the outer 

 extremity of the Gasserian recess (PL XXVIII. fig. 6, v."), which is apparent externally 

 in the angle between the dorsal extremity of the squamosal and the hinder margin of 

 the suspensorial portion of the fronto-parietal (PI. XXVIII. figs. 1 and 2, v."). The 

 foramen does not open directly on to the lateral surface of the skull, but into the 

 " Schlafengrube " (figs. 1 and 2, and PL XXIX. fig. 18, t.f. and v."), and through the 

 latter communicates with the exterior. The nasal branch of the ramus maxillaris 

 traverses a foramen (fig. 1) between the root of the upper labial cartilage and the 

 adjacent portion of the antorbital process, and then enters the nasal capsule. In its 

 course downward to" the lower jaw the ramus mandibularis runs parallel to the 

 anterior margin of the squamosal and in contact with the outer surface of that bone. 

 A small branch of this nerve disappears through a minute foramen on the outer surface 



