114 ANNALS NEW YORK ACADEMY OF SCIENCES 



The most typical attachment of this muscle is to the annulus of the ear 

 and to the pterygoid bone from the mandible. In spite of all the work 

 done on the pterygoids of mammals, one may say that they are of rather 

 unsatisfactory status as yet. Gaupp assumes that they are derived from 

 the parabasals and that they are not homologous with those of other mam- 

 mals. It is hoped that the problem will be solved as a result of Watson's 

 recent studies on the development of the skull in the monotremes. 



Presence of the detrahens mandibulce. — This pair of muscles serves as 

 the depressor of the mandible in monotremes where the digastric is en- 

 tirely absent. It originates on the mastoid and squamosal region of the 

 skull, wraps around the lower part of the head, and is inserted on the 

 lower edge of the mandible with a good attachment on the sides, so that 

 it has a firm hold. It is peculiar to the monotremes and is not homolo- 

 gous with the parieto-mandibularis (depressor mandibula?) of reptiles 

 which has a similar position and function. The reptilian analogue is 

 innervated by the seventh nerve, while the detrahens mandibulse in mono- 

 tremes is innervated by the trigeminus. Schulman, Toldt, Bijvot and 

 Gaupp believe that it belongs to the dorsal muscles of the head. Gaupp 

 and Schulman both believe that it is a slip of the capiti-mandibularis 

 ( masse ter portion) of the reptiles that has slipped back to act as the 

 depressor. The earlier investigators thought that it was a part of the 

 mammalian digastric, as they did not know of the nerve supply. All of 

 these investigators have changed their opinion with the working out of 

 the innervation by Schulman, who showed that it is innervated by the 

 trigeminus nerve. Schulman says : 



Es unterlie.ct somit meiner meimiug nach keinen zweifel. dass der M. de- 

 trahens maudiltuLie zu den dorsalen Kaumuskeln gehort, uud keinen Bauche 

 des M. digastricus mandibulre der hoheren Mammalia homolog ist. 



The meaning of this musculature in the monotremes seems to be that 

 the reptilian articulation of the mandible to the jaw w^as lost, as the 

 Eeichert Theory would assume, and that in the shifting of the muscles 

 in monotremes the new depressor was developed from the capiti-mandib- 

 ularis instead of from the depressor mandibulse or its mother mass. This 

 would place the monotremes in a different line, and their anatomy justly 

 places them at some distance from the rest of the mammals, so perhaps 

 this conclusion is not far wrong. 



