prootic fenestra 

 orbitoparietal commissure 

 foramen pseudoptica 

 orbitonasal fissure 

 crista galli, 

 foramen epiphoniale, 



OS carunculae 

 fenestra narina 

 nasolacrimal incisure 



zona annularis^ foramen infraconcha 



B M 



fused tips of Meckel's cartilages 



parietal lamina 



synotic and posterior tectum 



occipital condyle 



malleus part of Meckel's cartilage 

 ■hyoid arch 

 ceratobranchials 1-1 



fenestra narina 

 zona annularis. 



epiphanial foramen 



olfactory foramen, 

 preoptic pillar 

 foramen pseudoptica 

 antotic pillar, 

 alar canal 



synotic and posterior tectum 



palatine proces; 



crista galli 

 jomina orbitonasolis 

 orbital cartilage 



OS carunculae 



opening for duct of Jacobson's organ 



paraseptol cartilage 



olfactory foramen 



orbitonasal fissure 



carotid foramen 



Meckel's cartilage, 

 malleus. 



incus 

 stapes 

 fenestra ocustica 



endolymphatic foramen 



occipital condyle 



processus alaris 



tegmen tympani 



fenestra vestibuli 

 perilymphatic foramen 



■ metotic fissure 



Figure 3-15. Chondrocranium of 1 22-mm embryo of Plotypus. A, lateral view; B ventral v^w of 

 tip of Meckel's cartilage; C, dorsal view with port of cron.al roof removed; D, ventral v,ew with most 

 of Meckel's cartilage removed. (Modified from DeBeer, 1937) 



in the occipital arch; instead this foramen is confluent with 

 the jugular foramen, into which also opens the fenestra 

 perilymphaticus. 



The paroccipital process has a small tegmen tympani and 

 forms a lateral margin to the tympanic fossa. The hyoid 

 attaches to this margin lateral to the fenestra vestibuli. 



There is a broad orbitoparietal commissure, and from the 

 orbital plate there is a posteroventral antotic pillar and a 

 ventral preoptic pillar. The pila antotica attaches at the sides 

 of the dorsum sellae. The broad preoptic pillar attaches to 

 the trabecular stem behind a slight interorbital septum lead- 

 ing up and forward to a knob-like crista galli. To either side 

 below the crista galli is a large, round olfactory foramen; a 

 cribriform plate is not formed. The nasal capsule is solid 

 above and laterally, except for a small foramen epiphaniale 



at the end of the sphenethmoid commissure of the orbital 

 plate, and a nasolacrimal foramen on the same vertical but 

 near the ventral margin of the lateral wall of the capsule. 

 The hind wall of the capsule, the lamina orbitonasalis, is 

 fused with the midline plate and lacks any flooring. Ante- 

 riorly there are paired fenestrae narinae separated by a thin 

 and fenestrated septum. The margins of these fenestrae 

 show dorsal and ventral processes that join and more nearly 

 enclose the fleshy external naris. There is a broad zona an- 

 nularis formed by the lamina transversus anterior between 

 the marginal processes. The paraseptal cartilages attach to 

 this transverse connective and extend posteriorly as vertical 

 plates curving outward above and below the Jacobson's 

 organ and its Stenson's duct. Anteriorly the duct is enclosed 

 by the paraseptal cartilage opening ventrally at its anterior 



56 • OSTEOLOGY AND THE MAMMALIAN HEAD SKELETON 



