OF BAL^NOPTERA MUSCULUS, 209 



it overhangs tlie squamous, and in front by a smaller one which articulates with the lachry- 

 mal. The under side is concave, forming the roof of the orbit. The distance in a straight 

 line between its prominent extremities is 9 inches. The concavity is soon increased into a 

 groove which runs into a canal reiDresenting the continuation of the optic foramen (PI. vi, 

 fig. 2/). This forms a prominent ridge along the posterior border of the inferior aspect of 

 the orbital plate. The greater part of the remainder of this surface of the plate is hid- 

 den by the superior maxillary. There is a depression towards the base. 



The Ethmoid. — This bone is not easily studied owing to its position, and has in this case 

 suffered a good deal on account of its softness. It probably was never very distinct from 

 the rostral cartilage. There is now to be seen an irregular crumbling bone, filling the pos- 

 terior end of the cavity between the plates of the vomer. A plate passes upward from 

 either side to meet its fellow in the middle, on the under surface of the frontal. This may 

 perhaps be considered the orbital surface, though it is very deeply placed. In the B. ros- 

 trata (loc. cit.) it is said to reach as fiir back as the pterygoid bone ; in this case it does 

 not approach it. At the junction of these plates the bone spreads out laterally for a short 

 distance, supporting the frontal. 



The Vomer (PI. vi, fig. If, fig. 2 g). — The vomer consists of a horizontal portion fit- 

 ting on to the base of the skull, and of two plates forming the rostrum. The former portion 

 rests on the basispheuoid, and curves downward on either side to meet the internal edge of 

 the pterygoids. It is most expanded at the posterior end, measuring 10 1-2 inches in a 

 straight line between the angles. It begins to contract almost at once, but expands in 

 front of the pterygoids to meet the palatals ; still more anteriorly it bends upward and joins 

 the frontals. A little more than an inch in front of the posterior edge a median ridge 

 begins to appear, which soon becomes prominent, and sweeps boldly downward to form the 

 beginning of the rostrum. Towards the end of its course it turns suddenly backward, so 

 that the spine of the rostrum overhangs its posterior edge. The entire length of the 

 vomer is 10 feet 1 inch, that of the spine of the rostrum 9 feet. The two plates meet at 

 first at a very acute angle, which becomes more obtuse towards the apex. The greatest 

 depth of the bone is in the neighborhood of the anterior end of the palatals, where it 

 amounts to 13 inches. The superior edges of the plates, at first tliiu, become thick in the 

 nasal region where they articulate with the superior maxiUaries, but become anteriorly very 

 thin and scale-like. 



Palatal Bone (PL vi, fig. 2 A). — This bone consists of a thin plate lying on the outer 

 side of the vomer. The posterior end is the most solid part and articulates with the anterior 

 edge of the pterygoid; it reaches superiorly into the angle between that bone and the 

 frontal, and then expands on the under surface of the latter. From the lower end of the 

 pterygoid the border passes inward to meet the projecting spine at the beginning of the 

 rostrum of the vomer. The remainder of the lower border measures nearly 26 inches. On 

 reaching the supramaxillary the border turns upward and passes into the superior one by a 

 rounded angle. The anterior part of the superior border is marked by a deep groove for 

 the maxilla. Near the posterior superior angle there is also a slight groove passing down- 

 ward and backward with an elevation below it. 



Superior Maxilla (PL vi, fig. 1 cj, fig. 2 i). — This is best considered as a p^Tamid with 

 a superior, an internal, an inferior surface and a hollowed base for its posterior attachment. 

 The greatest length is 9 feet, to which about 2 inches may be added owing to injury of the 



JIEMOIRS BOST. 80C. NAT. HI8T. VOL. II. 63 



