asol capsule olfactory nerve foramen 



nasohypophyseal opening — C— 



area of attachment 



of posterior tectal cartilage 



orbital cartilage °>'"^ capsule 



IV,V,VI 



endolymphatic foramen 



neural arch 



ventral root foramen 

 of 1st spinal nerve 



t-rv?I=r — chordal rod 

 notochord 



subocular arch 

 orbital cartilage 



styloid cartilage 

 hypophyseol fenestra 



neural arch 



■chordal rod 



notochord 



notochord 



Figure 5-25. Endocranium of the lamprey. A, anterolateral view with port of nasol and otic 

 capsules cut owoy; B, dorsal view with left half of nasal capsule removed; C, ventral view. 



The nasal capsule is thin-walled and is separated from 

 the rest of the endocranium. It encloses the posteroventral 

 half of the nasal sac and is perforated by two large olfactory 

 foramina separated by a rather thick strut. 



Attached to the endocranium is a subocular arch. From 

 this arch a styliform process extends down to the side of the 

 pharyngeal cavity. Its tip is attached by fibrous cartilage to 

 the cornual cartilage extending forward below the pharyn- 

 geal cavity alongside the piston cartilage. Medial to the 

 styliform processes lie small velar cartilages, which join 

 below the pharyngoesophageal tube to support the anteri- 

 orly projecting fingers of the velum. 



The anterior end of the basitrabecular plate articulates 

 with the posterior tectal cartilage. From the lateral margins 

 of this, ethmoid processes extend ventrolaterally and 



slightly forward as part of the subocular arches. The distal 

 end of the ethmoid process is joined by soft cartilage to the 

 posterior lateral cartilage. 



In front of and overlapped by the posterior tectal cartilage 

 is an anterior tectal cartilage. This has bilateral oral proc- 

 esses, which extend posteriorly and down on either side to 

 attach to the general tissue mass above and medial to the 

 bases of the spinous cartilages. Just anterior to the oral 

 processes lie the small anterior lateral cartilages, which are 

 closely bound into the general supporting mass of the tip of 

 the tongue apparatus. 



The anterior tectal cartilage overlaps the annular carti- 

 lage of the oral sucker. The annular cartilage supports an 

 anterior pair of teeth and a semicircle of eight posterior 

 teeth. Posterolaterally spinous cartilages (stylets) extend 



!50 



THE HEAD SKELETON OF FISHES 



