MARYLAND TOSSIL PORPOISE KEULOGG. 



11 



and continue in contact to the apex of the above-mentioned indenta- 

 tion at the tip of the rostrum. The premaxillae thus completely roof 

 over the mesorostral gutter throughout most of its length. They 

 diverge posteriorly and commence to spread apart, as remarked 

 above, at a point 165 mm. anterior to the maxillary notches. The 

 mesorostral channel is thus exposed for a distance of 160 mm. in 

 front of the anterior end of the presphenoid. The raised convex 

 portions of the premaxillae are widest just anterior to the pre- 

 maxillary foramina and taper rapidly as they approach the level 

 of the nasal passages, and disappear slightly posterior to the supra- 

 orbital processes of the frontals. 



There are three pair of foramina on the distal one-third of the 

 rostrum. No trace of similar foramina can be found in the skull 

 of Lipotes^ though they are present in Inia^ but are irregularly 

 placed and are found as far back as the maxillary notches. Since 

 tliese foramina are present in pairs, measurements were taken and 

 their relative positions are shown in the following table: 



Position of the Paired Foramina near tip of Rostrum. 



The suture between the maxilla and premaxilla becomes obliterated 

 in front of the third pair of foramina. A shallow groove extending 

 forward leads from either of these foramina and follows the assumed 

 line of fusion of maxilla and premaxilla ; these grooves terminate be- 

 hind the second pair of foramina. The grooves for the second pair 

 of foramina are very short, but those for the first pair are well 

 defined and rather deep. The latter terminate on either side anterior 

 to the third tooth. The left premaxillary foramen is large (greatest 

 diameter 7 mm.) and is situated approximately 48 mm. in advance 

 of the nearest maxillary foramen. A broad and deep groove extends 

 backward from each premaxillary foramen and crosses the pre- 

 maxilla in an oblique course from internal to external margins, ter- 

 minating at or near the level of the posterior face of the supraorbi- 

 tal process of the frontal. There are several small maxillary fora- 

 mina on the left side of the skull, but only one can be found on the 

 right side. 



The vomer apparently increases in width posteriorly, but, as the 

 rostral extension of this bone is concealed for the most part by the 



