Osteology of Loxomma Allmanni. 43 



These bones do not exist in the Crocodilia or in the great 

 majority of fishes, though they are present not only in Loxomma 

 and Archegosaurus but also in Pteroplax • they do not appear 

 either to form a part of the skull in any other of the Labyrin- 

 thodonts. Occasion will be taken to notice these bones more 

 at length under Section III. Occipital Surface. 



The mastoids, which are squares of f inch, and form the 

 posterior external angles of the upper middle cranial surface, 

 lie external to, and join with, the last noticed bones ; in 

 front they abut upon the squamous bones ; externally they 

 are free, and bound the posterior part of the inner margins of 

 the fossa? leading to the ears. 



At the back part of the mastoids, and close under their 

 external angle, is a somewhat obtusely pointed tooth-like 

 process, directed backwards from the under surface of the 

 bone, and marked by muscular impressions. 



Tke squamous bones, of an irregular shape, lie external to 

 the parietal, and form the anterior curved margins of the tem- 

 poral fossae, having the postorbital and the supratemporal 

 (Huxley), the tympanic (Von Meyer), on their outer side. 

 They are connected in front with the postfrontal and post- 

 orbital, and behind with the mastoids. By a small posterior 

 part of their inner margins they are sutured to the so-called 

 " supraoccipitals." 



The postorbitals are of a somewhat rhomboidal outline ; their 

 anterior internal borders, concave, form the posterior and ex- 

 ternal margins of the true orbits ; their inner angles, which are 

 truncated, abut upon the postfrontals, which bound the orbits 

 posteriorly and internally. These two bones (the postorbital 

 and postfrontal), with a small portion of the posterior end of 

 the prefrontal, form the whole of the bony margin of the true 

 orbit. The anterior angles of the postorbitals project into the 

 orbital vacuities, marking on their outer margins the boun- 

 dary of the true orbit, as noticed already under the heading 

 " orbital vacuities.'' 1 The postorbitals articulate by their 

 inner and posterior sides with the squamous, and by their 

 outer and posterior with the supratemporal of Huxley, the 

 tympanic of Von Meyer. Their remaining sides, the anterior 

 and the external, join with the jugal bones. 



The molars or jugals, much elongated, form the middle 

 two thirds of the external borders of the orbital vacuities (on 

 the right side the bone, as already noticed, has been partially 

 dislocated), and overlap by their external borders nearly 6 

 inches of the borders of the maxillaries : they grow narrower 

 as they extend forward, and have a pointed end received into 

 the angle formed by the diverging posterior edges of the max- 



