Mar., 1903.] Spelerpes longkaudus. 387 



the ceratoliyal cartilage, just outside of the origin of M. hypo- 

 branchiahs, and sending its fibres inward to the extremity of the 

 opercuhnn. The function of the muscle is to raise the opercular 

 fold and to create thus a suction through the gill slits. There is, 

 of course, no homologue of this muscle either in Rana or in 

 Cryptobranchus. 



M. Levator arcuum branchialium. — (Plate 11, Fig. i, 

 mla. ) This slender and insignificant muscle arises as a fasciculus 

 of M. longissimus dorsi. It is given off from that muscle at the 

 extreme posterior end of the otic capsule and extends posteriorly 

 and obliquel}^ downward to an insertion on the first epibranchial 

 bar. It serves to raise the branchial apparatus. 



M. Constrictor arcuum branchialium. — Plate 11, Fig. 3, 

 mca., nice., mci.) This muscle is divided into three equal parts, 

 which, from a common origin, separate and run to three distinct 

 and different insertions. The mu.scle itself is a continuation or 

 prolongation of the fibres of M. hypobranchialis, and takes its 

 course along the inner or body side of the arches. Its first fasci- 

 culus is inserted on the course of the second epibranchial cartil- 

 age, its second fasciculus on the the third epibranchia and its 

 third part along the course of the last arch. Its evident function 

 is the closing of the branchial clefts, acting with M. cerato- 

 branchialis to create a suction of water through the clefts. 



M. Depressor arcuum branchialium. — (Plate 11, Fig. 2, 

 mdb.; Fig. 3, mab.) This muscle is a sheet of fibres arising on 

 the inner side of the last branchia and sending its fibres inward to 

 mingle in the middle line. The main part of the muscle is just 

 anterior to the tracheal opening, and .some of its fibres even mingle 

 with those of the following muscle. The name of the muscle 

 indicates its function. 



INI. Omohvoideus. — This is a rather small and insignificant 

 muscle at this stage. It arises in the region of the future scapula 

 and sends its fibres downward to mingle around the trachea. This 

 muscle does not function before the metamorphosis, and as no sign 

 of a scapula appears, it cannot now be traced to a definite origin. 



BODY muscles. 



The two body muscles which appear at the present stage are 

 the M. longissimus dorsi, and M. rectus abdominis. 



M. Longissimus DORSI. — (Plate 11, Fig. i, mid., mli.) This 

 large and important muscle has a double origin. The first is on 

 the auditory capsule, on the dorsal side next to the surface, and 

 in the region of the articulation of the jaw and of the eighth 

 nerve. The second origin is considerably posterior to the first and 

 is at the ba.se of the brain, on the parachordal cartilages. From 

 their origins, both fasciculi run directly tailwards, uniting in the 

 region of the tenth nerve, to form a dumb-bell-shaped muscle 

 which partially surrounds the medulla. After this point, the 

 muscle rapidly increases in size, as it runs on back toward the tail. 



