1883.] APPARATUS OF THE TENUIROSTRES. 67 



the serpi-hyoid are to be considered as a shifted origin, or as the result 

 of an expanding broadened insertion, I am yet unable to decide. 



M. stylo-hrjoideus arises as a broad flattened-out band from the 

 upper margia of the occiput, its origin being situated laterad from 

 the end of the thyro-hyal or great cornu of the same side. The 

 muscle then passes underneath (covered by) the parotic gland, crosses 

 the two ribands of the genio-hyoideus of the same side, being 

 directed obliquely forwards and inwards, and is inserted on the sides 

 of the basihyal, laterally and dorsally from the greater cornu. This 

 muscle, having its punctura fixum at the occiput, acts as the chief 

 retractor of the tongue. 



M. genio-hyoideus consists of two parts, both of which arise as 

 barrow flat bands from the border and inner margin of the mandi- 

 bles, being thus the most superficial muscles of all on the ventral side 

 between the mandibles. The two bands pass directly backwards 

 along the inner margin of the under jaw, then pass dorsally over the 

 stylo-hyoid and serpi-hyoid. The median portion attaches itself to 

 the distal three quarters of the cerato-branchial, by surrounding 

 or enveloping this bone, being only loosely fastened to it by con- 

 nective tissue. The outer part accompanies the cerato-branchial 

 throughout its length on the dorsal surface, and is attached to its 

 tip. Both these portions, constituting the genio-hyoid muscle, are 

 surrounded by a common slippery sheath, which compels them to 

 act exclusively in the direction of the bone. 



The muscle has its punctum fixum at its origin at the mandibles, 

 and consequently by its contraction protrudes the tongue. As the 

 cornua of the tongue, surrounded by the genio-hyoid muscle, might 

 be compared to a rod surrounded by an elastic steel spiral fastened 

 to one end of the rod, it will be understood that the force with 

 which and the extent to which the tongue can be propelled depends 

 directly on the length of the cornua. This agrees with observation, 

 e. g. Trochilus and Picus compared with Zosterops. 



M. cerato-glossus. This muscle arises from the distal two thirds of 

 the outer and upper aspect of the thyrohyal, and is attached to the 

 ventral surface of the basihyal. By its contraction it causes the 

 basi- and thyrohyals to be bent at an angle, and thus directs the tip 

 of the tongue. 



M. tracheo-hyoidexis arises from the latero-ventral aspect of the 

 upper part of the trachea, and is inserted into the dorsal surface of the 

 end of the basihyal bone by the help of a long and slender tendon. 

 This muscle acts as a retractor of the tongue when acting at the 

 time with its fellow on the other side ; but when acting singly it 

 directs the tongue to the right or to the left. 



Prosthemadera. 



The muscular apparatus of Prosthemadera exhibits some remark- 

 able differences from the arrangement of the muscles described 

 above. 



The mylo-hyoid muscle is not attached to any part of the tongue, 

 but (at least in my two specimens) is separated from it by a thick 



5*" 



