Lamprey Skeleton Type - The entirely cartilaginous skeleton of the lamprey is not particularly well developed. Study the skeletal elements in prepared specimens, which are usually embedded in acrylic. The head skeleton is complex and quite unlike that of other vertebrates.
 |
| Lamprey Skeleton Type |
Endochondral elements forming a chondrocranium include large cartilages that partially enclose the brain and sense organs (nasal capsule, otic capsule), and others that extend anteriorly to support the annular cartilage, the ring-like structure that is the main skeletal element of the oral funnel (see below). Several of these cartilages are labeled in. The median lingual cartilage, supporting the rasping tongue, extends posteriorly from the annular cartilage, ventral to the chondrocranium.
Extending posterior and connected to the chondrocranium is a network of cartilages forming the branchial basket, which supports the pharyngeal region. The somewhat hemispherical cartilage at the posterior end of the branchial basket is the pericardial cartilage, which lies on the posterior wall of the pericardial cavity, the space that contains the heart. There are three main differences between this pharyngeal skeletal support and that found in more derived fishes. One is that the structure is a connected network, rather than relatively separate and articulated arches. Another difference is the connection to the pericardial cartilage. Yet another is that the branchial basket lies superficially, lateral to the gills and thus just beneath the skin. In contrast, in other fishes the branchial arches lie more deeply, medial to the gills, and thus in the medial wall of the pharynx. Because the branchial basket lies just under the skin, it may be observed by carefully skinning one side of the head of your specimen. If you wish to do this, postpone your dissection until you have studied the remaining lamprey structures described below.
The large notochord is the axial support of the body. It is an elongated rod extending from beneath the posterior half of the brain to the tip of the tail. The vertebrae are represented by small, cartilaginous structures, termed arcualia, that lie dorsal to the notochord on either side of the spinal cord (see below). They are usually embedded in connective tissue or lost in prepared specimens, and are not particularly evident. Indeed, they are difficult to find, but may occasionally be observed in cross sections.
Posting Komentar