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the anterior Prolongation passes along the lateral surface of the maxillary process of the palatine, 

 and then turns mesially beneath that proeess, between it and the lining membrane of the roof of 

 the mouth cavity, and abuts and terminates against the lateral (distal) surface of the ascending 

 process of the maxillary. 



From the mesial or dorso-mesial surface of the mesial leg of the U-shaped sac the mesial divertic- 

 ulum has its origin, this diverticulum being formed of a noticeably delicate and very flexible mem- 

 brane. It lies against the lateral surface of the rostral, has a short anterior Prolongation between 

 the rostral and the mesial surface of the ascending process of the maxillary, and a longer posterior 

 Prolongation which extends around the hind end of the rostral, and there meets, but in the adult, 

 so far as could be determined by dissection, does not communicate with the corresponding divertic- 

 ulum of the opposite side. In 45 mm specimens the diverticula are apparently here in large and 

 free communication with each other. From the disposition of the diverticula, it is evident that when 

 the mouth is protruded and retruded the capacity of the nasal sac is first considerably enlarged 

 and then diminished, the circulation of the water in it thus being facilitated, as Kyle has stated. 



NASAL. 



The nasal is a small bone, which, by a downwardly projecting portion of its hind end, fits 

 against and is firmly attached to, the lateral surface of the mesethmoid process. It encloses the nasal 

 portion of the supraorbital latero-sensory canal, and bears, on its hind end, the nasal spine. From 

 its anterior end the naso-maxillary Hgament arises, and running forward and downward is inserted 

 on the ligamentary process of the maxillary. On its inner surface, near its hind end, and also on the 

 adjacent ligamentary surface of the mesethmoid process, the ethmo-maxillary Hgament and the 

 small rostro-nasal branch of the large palato-rostral ligament both have their attachments. 



FRONTAL. 



The frontal touches, in the mid-dorsal line, throughout nearly its entire length, its fellow 

 of the opposite side. At its anterior end its lateral edge rests upon the dorsal surface of the ecteth- 

 moid, its mesial edge restmg upon the dorsal surface of the pointed posterior portion of the meseth- 

 moid. In the anterior half of the orbital region, its mesial edge rests upon the dorsal edge of the 

 interorbital septum, that septum being a thin wall, cartilaginous in its anterior but membranous in 

 its posterior portion. In the posterior half of the orbital region a thin flange-like process has its origin 

 from the ventral surface of the frontal, the line of origin of the process running, at first, backward 

 and but slightly laterally, and then turning laterally, in a rounded angle, toward the postorbital 

 corner of the lateral edge of the bone. From this line of origin the flange projects downward, back- 

 ward and mesially, beginning at nothing anteriorly, increasing gradually in depth until it reaches the 

 rounded angle of its line of origin, and then diminishing again almost to nothing shortly before it 

 reaches the postorbital corner of the bone. The ventral edge of the anterior half of the flange, that 

 is, up to its deepest point, gives attachment to the dorsal edge of the membranous posterior half of 

 the interorbital septum; the flanges of opposite sides, which touch in the middle line throughout a 

 part of this distance, enclosing an anterior portion of the cranial cavity. Posterior to its deepest 

 point, the flange, turning laterally, overlaps externally and lies closely against the external surface 

 of the dorsal half of the alisphenoid, the base of the flange resting against the external surface of the 



