322 ANATOMY OF VERTEBRATES. 



in size the glenoid process, which it meets at a right angle, and 

 from the union of which the zygomatic process is continued for- 

 ward to join the malar process of the maxillary : there is no dis- 

 tinct malar bone. The parietal, ib. 7, is long and large, undivided 

 by a sagittal suture, from the place of which a bony falx is 

 developed internally, fig. 204, b. The frontals are small, and in 

 fig. 205, h, h, retain the frontal suture. The nasals, ib. 7i, n, are 

 long and large : they contribute to the rim of the orbit, and form 

 the posterior half of the large bony nostril, p. The maxillary, ib. 

 m, 2£iQv sending off a process which curves over the antorbital 

 foramen, extends forward, diverging from the nasal to form the 

 angular fissure which receives the premaxillary, o, 22. Each of 

 these bends inward at the anterior extremity, but is separated 

 by a wide space. There is a small prenasal ossicle at p, fig. 205, 

 and Z>, fig. 204, a. The vomer forms a bony vertical septum 

 dividing the nasal cavity from the presphenoid forward. The 

 palatine plate of the maxillary, fig. 204, a, 21, is pierced by large 

 oblique canals for the transmission of palatine branches of the 

 trigeminal nerve. The bony palate is continued backward entire 

 between the large shallow alveoli, ^, h, of the upper horny molars 

 to the posterior nostrils, i, which resemble those of the Crocodile 

 in their backward position. The sutures defining the palatines 

 and pterygoids are soon effaced. 



The Ornithorhynchus differs from the Echidna in the large 

 vacuities behind and in front of the tympanic cavity, the one 

 representing the combined jugular and precondyloid foramen, the 

 other the foramen ovale. The notch above the foramen magnum, 

 fig. 204, c, is better defined ; as is also the orbit. 



There is a small lacrymal foramen at the anterior and inner 

 part of the orbit in both the genera of Monotremes ; a little 

 loAver down is the commencement of the antorbital canal. This 

 canal branches in the Echidna, and terminates on the outer side 

 of the maxillary bone by a succession of small foramina ; but in 

 the Ornithorhynchus, Avhere it transmits a much larger sensi- 

 tive nerve, it divides into three canals, of which one emerges 

 beneath the uncinated process of the maxillary above mentioned ; 

 a second descends and opens upon the palate ; and the third 

 passes forward into the substance of the facial fork, and termi- 

 nates by a large foramen at the outside of the premaxillary bone. 



On the exterior of the cranium the ridj^es indicatino^ the extent 

 of the temporal muscles are clearly developed in the Ornitho- 

 rhynchus, and correspond with the stronger zygomata and the 

 more complete apparatus for mastication in this Monotreme. 



