ART. 15 ANATOMY OF THE EARED AND EAELESS SEALS HOWELL 45 



muscle was considerably heavier and the point of origin is marked 

 by a relatively deep fossa, but this is not present in all the Phocidae. 

 Insertion was into the mystacial pad deep to the naso-labialis. 



M. mandibalo-auricularis was a complex of several minute and slen- 

 der muscles which were not separated. Origin was from the dorsal 

 surface of the zygomatic root of the squamosal craniad of the audi- 

 tory meatus, while insertion, seemingly more intricate in Zalophus, 

 was about the auditory tube where this reaches the body surface. 



2. MASTICATORY MUSCDLATURE 



M. masseter (figs. 4, 5, 6) was partially divisible in the Zalophus 

 into two portions. The more superficial arose from the cranial third 

 of the zygomatic arch and was inserted along the border of the 

 mandible ventrad of the masseteric fossa, from just rostrad of this 

 to the tip of the angular process. The deeper portion was insepara- 

 ble craniad from the more superficial, and origin extended caudad as 

 far as the tip of the jugal. Insertion was into the entire masseteric 

 fossa of the mandible ventrad of the base of the coronoid process. 

 In the Phoca this muscle was completelj^ divisiblt, the more super- 

 ficial arising from the full extent of the jugal, with insertion along 

 the caudo- ventral border of the mandible from just rostrad of the 

 angular process almost to the condyle. The deeper part arose simi- 

 larly from the rostral end of the jugal caudad to the capsular liga- 

 ment of the glenoid fossa. Insertion was upon the whole caudo- 

 ventral half or more of the masseteric fossa of the mandible. 



M. temporalis (figs. 2, 3, 6) of the Zalophus was divisible along its 

 posterior portion into a superficial and a deep part. The former 

 arose by aponeurosis from the medial border of the temporal fossa, 

 rapidly thickened, and was inserted upon the lateral surface of the 

 coronoid process, its more superficial fibers beneath the zygoma 

 blending with the adjoining masseter. The deeper part arose from 

 the entire temporal fossa and inserted upon the medial surface of 

 the whole coronoid process. In the young animal dissected the tem- 

 porals did not yet approach the middorsal line. In the Phoca the 

 temporal was not divisible and was very much weaker and less exten- 

 sive. Insertion was for a short distance upon the lateral, and upon 

 the entire medial surface of the coronoid process. 



M. pterygoideus externus (figs. 4, 5) arose in the Zalophus from the 

 bony bridge over the alisphenoid canal, with insertion upon the 

 roughened area directed cranio-mediad upon the medial condyle of 

 the mandible. In the Phoca the origin was analogous, from the 

 bridge of bone separating the foramina ovale and rotundum. Inser- 

 tion was more robust, rostro-ventrad of the condyle upon the medial 

 mandible. Miller found conditions similar in P. vitulina and Arcto- 



