— 57 — 



of the basioccipital by a narrow median slit-like opening, which extends the füll length of the groove 

 and forms the posterior half of the hypophysial fenestra. This fenestra, as already stated, is closed 

 ventrally, excepting in its posterior portion, by the underlying parasphenoid, the hind end of the 

 fenestra remaining uncovered, spreading somewhat, and so forming an opening which leads directly 

 into the hind end of the myodome. On the lateral surface of the hind end of the bone, immediately 

 dorsal to a horizontal plane through the center of the vertebra-like depression on that end, there 

 is, on either side, a slight depression which gives insertion to the occipito-supraclavicular ligament. 

 This ligament of fishes is said by Sagemehl ('84 b, p. 49) to be a differentiation of the perimuscular 

 fascia of the adductor niuscle of the Shoulder girdle; but this adductor muscle, as described by 

 Sagemehl in the Characinidae, is not found in Scorpaena, and I doubt greatly this origin of the liga- 

 ment. The only muscle that at all resembles SagemehPs descriptions of the adductor, is a flat, thin 

 muscle band that arises from the hind edge of the skull and has its insertion on the occipito-supra- 

 clavicular ligament near its outer end. 



The basioccipital is bounded anteriorly, on either side, by the proötic, with which it is in 

 synchondrosis, and dorsally by the exoccipital with which it is partly in synchondrosis, and 

 partly in sutural contact. Its ventral surface is overlapped externally and largely covered by the 

 parasphenoid. Its hind end is wholly occupied by the deep conical vertebra-like depression. 



EXOCCIPITAL. 



The exoccipital is an irregulär bone which forms part of the lateral surface and part of the 

 posterior surface of the brain case, this latter portion having a medullary Prolongation. The angular 

 edge that separates these two portions of the outer surface of the bone has, at about the middle of 

 its length, a pronounced reentrant and usually well rounded angle. Anterior to this angle the edge 

 extends dorso-anteriorly and, reaching to the level of the floor of the hind end of the temporal fossa, 

 forms the ventral portion of the lateral bounding wall of the posterior opening of that fossa. Posterior 

 to the angle, the edge extends posteriorly and but slightly downward, and is thickened to form, at 

 its hind end, an articular head, which looks posteriorly and slightly ventro-mesially, articulates with 

 a process on the anterior edge of the first vertebra, and may be called the condylar process of the 

 bone. The ventral surface of this condylar process is roughened, and rests directly upon the lateral 

 portion of the dorsal surface of the hind end of the basioccipital, the two bones enclosing, at the 

 anterior end of this suturating surface, the little nodule of cartilage already referred to when des- 

 cribing the basioccipital. Anterior to this part of the exoccipital, the ventral edge of the bone is a 

 thin plate which rests upon and slightly overlaps externally the dorsal edge of the thin lateral portion 

 of the basioccipital, the two bones forming the lateral wall of the saccular recess of the cranial cavity. 



That part of the exoccipital that forms part of the posterior surface of the skull is presented 

 dorso-posteriorly and is separated into two parts by a ventral continuation of the epiotic ridge, that 

 ridge forming the mesial boundary of the posterior opening of the temporal fossa. The medullary 

 Prolongation of this part of the bone looks dorso-laterally, arches over the canal for the medulla 

 oblongata, and is in contact, in the median line, with its fellow of the opposite side. This contact 

 is by thin external and internal laminae of bone, the space between these laminae being filled with 

 cartilage. Extending obliquely across this part of the bone there is a marked thickening which begins 

 below and extends dorso-posteriorly, presenting a process-like appearance and strongly suggesting 

 a vertebral arch here fused with the exoccipital. The dorsal end of this process-like thickening forms 



Zoologica. Heft ■>?. 8 



