Miscellaneous, 393 



the super-squamosal to the end of the upper and hinder angle. The 

 hind border of the squamosal is concave, and forms the fore part of 

 the " meatus auditorius externus :" the hinder half of the under sur- 

 face of the squamosal expands and is slightly excavated to articulate 

 yf'ith. the iftternal swollen condyloid end of the tympanic. 



The body of the tympanic is a small subcompressed stem ex- 

 panded slightly and truncate above, w^here it articulates with the 

 mastoid and supersquamosal. The outer border of the stem is 

 rounded and concave, forming the inner and hinder border of the 

 " meatus auditorius." The inner border of the tympanic joins the 

 mastoid and pterygoid. The lower end of the tympanic suddenly 

 expands into a large oblique suboval articular surface, convex from 

 before backwards, slightly concave laterally at its fore part. 



The articular element of the mandible is adapted to the hinder 

 half of this condyle ; the subangular element articulates with the 

 front half. 



The lacrymal forms the lower two-thirds of the anterior boundary 

 of the orbit, and sends off from the middle of its outer margin a 

 short plate or process protecting the lacrymal opening : the bone 

 contracts vertically as it approaches the nostril, of which it forms 

 the hind border, which is slightly concave. The upper border of 

 the lacrymal sends posteriorly a process which fits a notch of the 

 prefrontal, and anteriorly it reciprocally receives a process of the 

 prefrontal and also of the nasal. Inferiorly, the lacrymal unites 

 with the maxillary and malar. 



The two supplemental bones of the skull, which have no homo- 

 logues in existing Crocodilians, are the "postorbital*" and " super- 

 squamosal f;" both, however, are developed in Archegosaurus and 

 the Lahyrinthodonts. The post-orbital is the homologue of the 

 inferior division of the post-frontal, in those Lacertians (e. g. Iguana^ 

 TejuSy Ophisaurus, Anguis) in which that bone is said to be divided. 

 The post-orbital, in Ichthyosaurus, resembles most a dismemberment 

 of the malar ; its thin obtuse scale-like lower end overlaps and 

 joins by a squamous suture the hind end of the malar ; the post- 

 orbital expands as it ascends to the middle of the back of the 

 orbit, then gradually contracts to a point as it curves upwards 

 and forwards, articulating with the super-squamosal and post- 

 frontal. 



The super-squamosal may be in like manner regarded as a dis- 

 memberment of the squamosal ; were it confluent therewith, the 

 resemblance which the bone would present to the zygomatic and 

 squamosal parts of the mammalian temporal would be very close ; 

 only the squamosal part would be removed from the inner wall to 

 the outer wall of the temporal fossa. The super-squamosal, in fact, 



* Described as '* apparently a distinct and peculiar posterior bone " of the 

 orbit, in the ' Report ' of 1839. 



t The recognized distinctness of this bone in the skull of the Ichthyosaurus 

 inclined uie, in 1839, to tlie view of the zygomatic and squamous parts of the 

 " temporal bone " being distinct elements, — an error out of which I worked myself 

 in subsequent toihng at homologies. 



