On the structure and development of the skull of the common frog (Rana temporaria, L.) / by William Kitchen Parker.

  • William Kitchen Parker
Date:
[1871]
Catalogue details

Licence: Public Domain Mark

Credit: On the structure and development of the skull of the common frog (Rana temporaria, L.) / by William Kitchen Parker. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

    54/104 (page 184)
    compared with the embryonic skull of the Teleostean (Huxley, 'Croonian Lecture,' p. 29, fig. 8, and ' Elem. Comp. Anat.' p. 185, fig. 72), it will be seen that the hyo-mandibular runs almost directly fonuards, and that the boss to which the opercular is attached grows out a little distance below the posterior hyo-mandibular fork. Now the segmen- tation of the hyo-mandibular in the Frog takes place immediately below this boss, leaving it free; and from the first it has a direction ybra'«r(?5, which is only intensified and not altered in the adult. The medio-stapedial (m.sf.) has now all the appearance of the osseous auditory columella of the Lizard; it is twisted and curved somewhat, is very slender at first, and then bulges behind; it is bevelled at its end, towards the skull, and is slightly unossified at its edge behind. The bevelled inner face of the medio-stapedial articulates with the lower half of the outer face of the interstapedial, the segment which was taken from its base. This intercalary piece, the undoubted homologue of the mammalian os orbiculare, has now become a solid Avedge of hyaline cartilage, and has found lodgement in the anterior part of the deep stapedial fossa. The interstape- dial is pointed in front, has a convex upper, and concave posterior and lower margins; it is thick and solid, especially behind, where it articulates with the stapedial plate. The homology of the interstapedial is with the condyle of the posterior hyo-mandibular fork of the Osseous Fish ; its function is to connect the true stapedial (or auditory) segment with the medio-stapedial lujoid element. The periotic element, stapedial {st.), is elegantly elliptical in shape ; but the anterior margin is shortened, where it fits to the, subconcave face of the interstapedial (Plate VIII. fig. 9, st., i.st.); it is gently concave on the inner face, and is very thick and convex on the outer (Plate VIL fig. 15, st.) ; like the other parts of the middle ear, with the exception of the medio-stapedial, it is wholly unossified. It is attached to the edges of the fenestral fossa by a delicate band of fibrous tissue (see Plate VIII. fig. 10, where it is seen from within); but much of the inner face is in immediate contact with the cavity of the vestibule. The fenestral or stapedial fossa (Plate VII. fig. 16, st.f.) is beautifully egg-shaped and of considerable depth (see section, fig. 15); behind, the exoccipital [e.o.) keeps at some distance from its rim; but in front the prootic {]^>ro.) sends a small wedge of bone into its fundus. The fenestra ovalis (fs.o.) takes up the postero-inferior third of the fundus; it is reniform, with the concave edge looking obliquely forwards and upwards; it nowhere reaches the edge of the pit; the main otoconial mass (of.) can be seen through the fenestra. This operculated cleft in the periotic wall was once the size of the stapedial plate ; the floor of the pit has grown, Avhilst the stapedial plate has been thickening, as the creature has become full-sized. The stylo-hyal (st.Ji.) has its permanent attachment a short distance below the rim of the fossa at its interior third (Plate VII. fig. 15, Plate X. fig 9, st.L). The stylo-cerato-hyal band of cartilage has changed but little since the Frog was two or three months old; it has not become osseous (Plate IX. fig. 3, st.h. and Plate X. fig. 2). The hypohyal region {hy.li.) retains the lobe, both before and be- hind, which was seen in the Tadpole (Plate V. fig. 2): these lobes have now become