35^ 



TRANS. ST. LOUIS ACAD. SCIENCE. 



No. 2. 



monkey's lower jaw (NAT. SIZE), UNDER SURFACE. 



I. Anteriormass of muse, di'^'astrictis. 2. Posterior bellies of w/Mic. (//^fax/was. 



the belly. In the diagram, the triangular space between these 

 differently running fibres is represented as open ; in fact, there 

 was no such free space, the fibres being close together and held 

 in position by connective tissue. An accurate drawing of the 

 appearances was made from the dissected specimen. 



Since making this dicovery I have noted that in all the mon- 

 keys examined dying at the St. Louis Zoological Garden, the 

 two anterior bellies of the digastricus (which otherwise resem- 

 bles the normal human) form one continuous sheet of muscle, 

 as shown in the diagram. In these animals, however, there is a 

 tendinous arch continuous with the. tendons of the two digastrics 

 and crossing in front of the hyoid bone ; from this arch the fibres 

 of the anterior muscular mass take origin. 



The resemblance between this normal form of the digastricus 

 in the monkey and the human abnormity recorded is most strik- 

 ing, and will be regarded by some Biologists as a good illustra- 

 tion of " reversion of type." 



