TllK ^MANDIBULAR AND IIVOID MUSCLES OE MA.MMALS. 628 
wliicli gives rise to the stapedius, stylo-liyoid, and ])osterior 
digastric. This forward growth receives a secondary inner- 
vation from the fifth nerve, ddiese statements were adversely 
criticised by Bijvoet. 
-Ti<The above-recorded observations show that the depressor 
mandibnla) anterior of Ornithorhynchus, and its homologne, 
the anterior digastric of Dasynrns, pig and rabbit, are formed 
by proliferation from the ventral surface of the intermandi- 
bnlaris. 
"^On the Formation o f the Digastric Muscle. — Schul- 
man, followed by Bijvoet, came to the conclusion that the primi- 
tive condition of the anterior digastric mnscle is indicated by 
the depressor mandibulm anterior of Echidna and Ornitho- 
rbynchus,^ viz. a sheet of approximately transverse fibres 
below the intermandibularis, attached laterally to the lower 
jaw; that this transverse sheet became more longitudinal in 
direction, and that its hind end — the original inner end — 
gained an attachment to the transverse aponeurosis of the 
posterior digastric muscle. A condition similar to that of 
Bradypus tridactylus would i-esnlt, and from this all the 
varied forms of a digastricus verus and digastricus spnrius 
can be easily derived. 
Toldt^s theoiy of the phylogenetic development of tlie 
digastricus muscle differs from that of Schulman and Bijvoet 
in some particulars, and is as follows. The anterior digastric 
‘^‘besitzt urspriinglich, gleich dem M. mylohyoideus, den 
Character und die Bedeutung eines Eingeweidemuskels ; er 
ist die aussere Langsfaserschichte des Mundhdhlenbodens, 
angelegt der Querfaserscbichte desselben, dem M. mylo- 
hyoideus. This longitudinal muscle unites with a hinder 
longitudinal muscle innervated by the twelfth, to form a con- 
tinuous longitudinal muscle — the sterno-mandibularis, ex- 
tending from the sternum to the lower jaw. This condition is 
' Schulman, “ fiilirt die A'ereiiiiguiig des M. depressor mandiliula) 
anterior init voin N. facialis versorgten M. depressor maiidihulas 
posterior oder richtiger eineni hyoidealen Componenten des M. con- 
strictor zur Bildung eines wirklichen M. digastricus.'' 
