Frog skull parts2/10/2024 We will study three groups of bones the Occipitals, the Sphenoids and the Ethmoids. It can remain catrilage or become replacement bone. Neurocranium (Chondrocranium) is from neural crest cells and mesodermal mesenchyme. The bones we will concentrate on in this lab are listed here. Use the space below to draw the paired wolf dentary bones. Number of dermal bones in the alligator skull: The following drawings should provide an understanding of the trend towards loss of dermal bone ( Williston’s Law). If any bone is not listed as neurocranium or splanchnocranium on page 39, it is dermal in origin. Note that one pair of bones on one of the drawings is from the splanchnocranium and should not be counted. Please use only the drawings in this lab guide for the count. Count the total number of dermal bones (paired (X2) and unpaired (X1) in each species. Using the drawings and the skulls provided, identify the dermal bones in each skull. These bones are grouped as the facial (upper jaw, nose), v ault (front of skull), orbital (around eyes), temporal (side of skull), palatal (roof of mouth) and m andibular (lower jaw) series.Īlligator and wolf on display. Identify all of these dermal bones on the wolf skull and learn them. The dermatocranium contributions to the mammal skull that we wish to learn are all those bones that are labeled on the drawing of the wolf skull, plus the dentary bone of the lower jaw. In other animal groups the cartilage disappears and when you look down on the skull you are looking at the bones of the dermatocranium. See the dermal armour of Amia, the bowfin, which sits on the cartilaginous neurocranium. The dermatocranium forms most of the skull and functions as a protective shield for the brain. These are from dermatome (epimere mesoderm). The original dermal scales (or armour) of Ostracoderms sink down, attach to the neurocranium and are ossified to form dermal bones. In mammals, gill arches also form the elements of the larynx (hyoid bone, thyroid and cricoid cartilages). Look at the alligator and identify the quadrate and articular bones. The ossifications of the splanchnocranium of the teleost fishes cannot be readily identified on the wolf skull since they are either the framework for subsequent dermal tooth-bearing bones, or have moved from their association with the jaws to form the ear bones: quadrate (incus), articular (malleus) and hyomandibular (columella or stapes). Splanchnocranium of a cartilaginous dogfish and salamander The original branchial skeleton of cartilage came from neural crest cells. The gill arches serve to support the gills and offer a site for respiratory muscle attachment. The splanchnocranium consists of the gill arches and their derivatives. What happens with the original top of the box?ĭraw a stylized (rectangular) brain box and label the parts of the neurocranium. On either side, in the nostrils, is a complex of thin bones looking like swirls of flaky pastry. The front of the box is the perpendicular bone dividing the nostrils. W hat group of bones forms the bottom and sides of the box? What group of bones forms the back of the box? W hat group of bones has holes for the cranial nerves? What group of bones surrounds the opening for the spinal cord (foramen magnum)? The neurocranium bones are painted black on the demonstration wolf and cat skulls. They cannot be distinguished from dermal bone, since they differ only in embryonic origin. Note that these bones are endochondral (or replacement or nondermal) bones. Identify the bones of the neurocranium in the wolf skull provided, using the lab drawings, and table, and the painted skulls on demonstration. The cranial nerves punch through the sides of the box. The bones forming these regions are grouped as the occipitals, sphenoids and e thmoids. If we think of the entire skull as rectangular box, the bottom, back and sides of the box make up the neurocranium. The neurocranium is a specialized portion of the splanchnocranium and comes from neural crest cells and mesodermal mesenchyme. In the Elasmobranchs (sharks and rays) it is composed of cartilage (chondrocranium), but in most other vertebrates, the cartilage is replaced by bone ( endochondral or replacement bone). The neurocranium is the portion of the skull that protects the brain and certain sense organs. 1)For the three parts of the skull, be familiar with the following:ģ) Learn the different skull types based on temporal fossaeĤ) Understand the evolution of the secondary palateĥ) Learn how the splanchnocranium contributes to jaw suspension and evolution of the middle ear in vertebratesĪs discussed in lectures there are three elements that contribute to skull formation in the vertebrates:
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