THE SKULL OF CniM.KRA, 113 



figui'es. Thei'e would accordingly seem to be some error in this 

 figure 165. 



The ethmoidal cartilage, as shown in these embryos of Callo- 

 rJiynchus, arises from the trabecular plate posterior to the 

 fenestra olfactoria of its side, find runs dorsally and then 

 anteriorly to meet and fuse with the band-like dorso-lateral 

 trabecular process. At its ventral end the ethmoidal cartilage 

 gives off a lateral process which, even in the eai'liest stages shown 

 by Schauinsland, has already fused completely with the palato- 

 quadrate. The sphenola.teral cartilage grows forward dorsal to 

 the orbit, and in the 60 mm. embryo, where it is still pro- 

 cartilaginous, bifurcates antei'iorly, one end passing dorsal and 

 the other ventral to the ramus ophthalmicus superficialis tri- 

 gemini, which nerve includes the lateralis fibres destined to 

 supply the latero-sensory and ampuUary organs of the region. 

 The ventral one of these two ends of the sphenolateral cartilage 

 has already fused, in this embryo, with the ethmoidal carti- 

 lage internal to the ramus ophthalmicus superficialis, and the 

 dorsal end also later fuses with that cartilage but external to 

 the ophthalmicus superficialis, this nerve thus being enclosed in 

 a foramen and a dorso-lateral antorbital process being formed. 

 This process is called by Schauinsland the preorbital process, and 

 botli it and the postorbital process are said by him to be 

 primarily independent pieces of cartilage. Concomitantly with 

 the formation of this process and the related foramen, a roof of 

 cai-tilage has been formed over the nervi ophthalmicus super- 

 ficialis trigemini and ophthalmicus profundus, enclosing them in 

 a meilian canal called by Schauinsland the ethmoidal canal. This 

 canal is evidently formed by the coalescence, in the median line, 

 of two canals, one on either side of the head, each of these canals 

 being formed by the roofing over of the groove that, in the 

 Selachii, lodges the corresponding portion of the ramus ophthal- 

 micus superficialis trigemini. In certain specimens of Chlamydo- 

 sdachus I find these grooves partially roofed, either by lips of 

 cartilage that project toward each other from the edges of the 

 grooves, or by nodules of cartilage suspended in membranous 

 strands that stretch across the grooves ; and if this roofing process 

 were to be completed and the groov^es so formed pressed together 

 in the median line, a median canal would be formed the roof of 

 which would form the actual roof of the cranium and its floor the 

 I'oof of the cranial cavity. 



A remnant of the fenestra pi'Pecerebralis of my descriptions of 

 the Selachii (Allis, 1913) is found, as will be later fully explained, 

 in the small median opening marked t in Schauinsland's figures 

 124 and 125, and said by him to be a " Spalte, welche das 

 Schiideldach von dem vorderen ethmoidalen Teil des Schiidels 

 trennt." The two large openings in the cranial roof that are 

 called by Schauinsland the aiiterior and posterior divisions of the 

 primarily single " Prfefrontalliicke," are not parts of the fenestra 



