fascia, is not the true suspensorio-opercular connection, which is correctly described by COPE,' as passing from the operculum to

Fig. 1.

Lhs.

Diagram from a drawing of the left side of a model of the skull of a

Necturus 49.5 mm. long.

a. Os articulare (angulare ?).

c.-Columella (operculum).

f.-Os frontale.

j.-Ramus jugularis VII.

6.-Nervus buccalis.

d.- Os dentare.
h.-Ceratohyale.

L. h.-s.-Ligamentum hyo-suspensoriale.

L. m.-h.-Ligamentum mandibulo-hyoidale.

L. s..e.—Ligamentum squamoso-columellare.

m. e. VII.-Ramus mandibularis externus facialis.
m. V.-Nervus maxillo-mandibularis trigemini.

m. i.-Ramus mandibularis internus facialis.
0.-Nervus opticus.

o. m.-Nervus oculomotorius.

o. p.-Ramus ophthalmicus profundus trigemini.
o. q.-Os quadratum.

0. S.- -R. ophthalmicus superficialis facialis. p. Os parietale.
pp. Os palatopterygoideum.

9.-Quadratum.

S.-Os squamosum.

ps.-Os parasphenoideum.

r. c.-Ramus communicans glossopharyngei. t.-Trabeculum.

the squamosum, who does not however, give the relation of the nervus facialis. DRÜNER has recently described correctly the relations in both Necturus and Proteus.

1 COPE, E. D. The Batrachia of North America. Bull. U. S. Nat'l. Museum, No. 34, 18.

The following description of the relations in a Necturus of 49.5 mm. length, based in part on a model of this stage (Fig. 1), will serve as a basis of comparison. The operculum at this stage is roughly oval in outline and slighly ridged along its long axis. At its cephalic end it is fused with the otic capsule, projecting backward into the fenestra vestibuli. From the cephalic end a dense ligament passes cephalad and dorsad to the os squamosum at about its middle point. The bone forms a slight curve, the convexity looking upwards, and it lies upon the external semicircular canal of the otic capsule, extending down over the otic process of the quadrate and becoming closely connected with a bone lying upon the external surface of the quadratum, and which it partly covers. This bone' I shall describe in another place. The squamoso-opercular ligament is attached to the under side of the squamosum where the bone passes from the ear capsule to cover the outer side of the processus oticus quadrati. At this stage the "stapedial" process of the squamosum present in the adult has just begun to develop. The ligament, in its course from the operculum to the squamosum, passes external (laterad) to the ramus jugularis facialis and the vena jugularis. The ramus jugularis passes outward and slightly backward, between the ligament and the vein to the dorsal edge of the former where it receives the ramus communicans glossopharyngei, which lies close to the ear capsule laterad to the vena jugularis. Beyond the point of the union with the ramus communicans, the jugular branch of the seventh passes outward, under the ventral edge of the squamosum to curve around the dorsal side of the otic division of the M. depressor mandibuli. The ramus mandibularis externus facialis from its ganglion which lies immediately outside the foramen for the facial nerve, in a depression just caudad of the

1 This bone arises in Necturus as a separate ossification, whose lower end subsequently is fused with or becomes the ossification of the quadrate. In Desmognathus and Spelerpes the same bone lies farther back, projecting under the squamosum, and in the adult forms the process of the quadrate named for the purposes of this paper the subsquamosal process.

processus basilaris quadrati, 'passes forward and outward under the quadratum to the outer surface of the squamosum, passing in front of (ventrad and cephalad to) the ligament.

The ramus palatinus which passes forward through a foramen distinct from that for the rest of the facial nerve, and the ramus mandibularis internus which passes immediately ventrad from the cephalic edge of the accessory lateral line ganglion, do not come into close relation to the columella, but are, of course, morphologically below and in front of it.

In an older Necturus, 9.4 c. m. long, the relations are as in the specimen just described, save that the processus "stapedialis" of the squamosum has attained an appreciable length, and the operculum possesses a short ossified stalk to which the liga

Fig. 2a.

Section of the Necturus embryo 19 mm. in length. c.-anlage of the squamoso-columellar ligament; h.-hyoid; v. j.—vena jugularis ; n. j.— nervus jugularis ; d. m.—M. depressor mandibuli; s.—squamosum. Fig. 2b. Same, three sections farther forward.

ment attaches.

Neither ossification appears to be an ossification of the ligament, but ossifications of the squamosum and operculum at each end of the ligament, acomplishing in that way the increase in length due to growth. In the adult, the operculum possesses an ossified process of some length joined

by ligament to the relatively long stapedial process of the squamosum.

That the relation of ligament to squamosum is a primary condition in this form and not a secondary modification, is seen in tracing the development of these structures. In an embryo 19 mm. in length (Fig. 2), the ossification of the squamosum is just beginning as a formation in a group of cells located upon the external semicircular canal of the ear. It extends down over the otic process of the quadratum covering with its lower (cephalic) end the upper end of a bone which is developed upon the external surface of the quadrate. At this stage, the operculum is just beginning to chondrify as a distinct center, and from it a cord of cells is continued forward, ventral to the vena jugularis and the ramus jugularis, to the cell surrounding the developing squamosum, becoming continuous with them a short distance (50) back of the processus oticus quadrati. The cells are of course continuous with those of the squamosum and also with the cells between that bone and the quadratum, so that the squamosum, the quadratum, and the ligament-anlage, may be said to be joined together by a common mass of cells. In the just hatched larva, likewise, the ligament-anlage, clearly goes to the under side of the squamosum and inserts itself between that bone and the processus oticus quadrati, so that it might be interpreted as going to both structures. As soon as the connective tissue fibers develop, however, the relation is seen to be with the squamosum and not with the quadratum. It is interesting to note the relatively early development of the ligament -practically at the same time as the squamosum and the operculum-later, however, than the chondrification of the chondrocranium.

Spelerpes bilineatus.

In this form, as well as in Desmognathus, the suspensorio-opercular connection possesses the same relation to the nervus facialis-that is, the nerve lies entirely cephalad and ventrad to the stilus columellae; in other words, under it. In relation to the jugular vein, the stilus possesses the same relation as the ligament described in Necturus-i. e. it passes ventrad to it.

In the adult Spelerpes (Figure 3), the stilus is cartilaginous with a perichondral ossification continuous with the ossification of the operculum;-the cartilaginous core of the stilus, however, is distinct from the ring of cartilage within the operculum.

Fig. 3. Spelerpes bilineatus, adult 67 mm. long. Section through the right otic capsule. c-Stilus columellae; o-oral cavity; v. j.-vena jugularis; d. m.-M. depressor mandibuli; S.-squamosum.

The stilus passes forward, upward and slightly outward to the lower edge of the squamosum with which its cephalic end is joined by connective tissue (Fig. 3), and also with a small cartilage which lies upon the ventral edge of the squamosum. This cartilage extends forward for about 150 microns and is cylindrical. It is free at its caudal end, which articulates with the stilus, and fused with the ventral edge of the squamosum. The stilus and operculum are at about the same level. The former lies at first upon the dorsal side of the external semicircular canal, gradually moving down to the lateral surface of the otic capsule, as it is traced forward. As it continues to