 to this first session on head and neck. So, as per request from all students, I am beginning with the head and neck sessions. In this session, we will be starting with the skull bone. Skull forms the basis of the head and neck and that is why we are starting with this bone. In the head and neck region, the bones which are included are one is the skull, then other is the cervical vertebrae which are seven in number, then hyoid bone. These are the bones included in head and neck. So, let us start with the skull. So, what is the difference between skull and cranium? At times, many students get confused pertaining to this topic and they consider both as synonymous. So, we should be knowing what is the difference between the skull and the cranium. What we can see in this image, this is the skull. Then what is cranium? If we remove the mandible, if mandible is removed, then whatever part of the skull is left, that is referred to as cranium. So, basically cranium is skull without mandible. With mandible, this entire thing is considered as skull. How to hold the skull in anatomical position? In anatomical position, the skull has to be held in such a way that this part is anterior, this part is posterior, superior and inferior. With both hands, you have to hold the skull. These two planes are important. Here, we can say this is the orbital margin. This is the inferior margin of the orbital foramen, this point and the upper margin of the external acoustic meiasis. This opening which we can see, this is the external acoustic meiasis. So, if we draw an imaginary line joining these two points, the inferior margin of the orbit and the superior margin of the external acoustic meiasis, this line is referred to as transferred plane. So, while holding the skull in anatomical position, it has to be held in such a way that these two points lie in one horizontal plane. There is one more line described with respect to the anatomical position of skull, that is Reed's baseline. In this, one point is constant, that is the inferior margin of the orbit and other point it passes through the middle of the external acoustic meiasis. For Reed's baseline, the posterior point is at the center of the external acoustic meiasis. Either of the two you can remember, but more preferably Frankfurt's plane is preferred for holding the skull in anatomical position. Now, let's see the parts of the skull. In general, skull can be divided into two parts. One is referred to as the cranial skeleton and other is referred to as the facial skeleton. Okay? Cranial skeleton is also referred to as neurocranium and facial skeleton is also referred to as viscerocranium. So, briefly you can get an idea of which part is cranial skeleton, which part is facial skeleton with these images. This is the lateral view and this is the anterior view of the skull. Okay? Facial skeleton is more on the anterior aspect. Okay? The remaining part of the skull is cranial skeleton. We'll see which all bones are included in these two parts of the skull. So, here we can see the bones forming the cranial skeleton as well as bones forming the facial skeleton. In all in the skull has got 22 bones excluding the ear ossicles. Okay? If ear ossicles are included, it becomes 28. There are three ear ossicles on each side. So, it will add six more bones. Okay? So, cranial skeleton, it includes pad bones and unpad bones. Pad bones are parietal bone and temporal bone. This is the parietal bone. This is the temporal bone. And unpad bones are frontal bone and behind there will be occipital bone and spinoid bone and ifmoid bone. These are unpad bones of the cranial skeleton. And facial skeleton, it has got total of 14 bones. Here also there are pad and unpad bones. So, we can remember the unpad. One is the mandible and other is the boomer. This is mandible and boomer is the midline bone. When we see the nasal cavity, the bone with a thin bone seen in the midline will be boomer. Okay? Other pariet bones in the facial skeleton are maxilla, zygomatic, nasal bone, lacrimal bone, palatine bone and inferior nasal conca. Okay? All these are included in pad bones of the facial skeleton. Okay? Here we can say this is the maxilla and this is the zygomatic bone. Here is the nasal bone. Okay? Lacrimal bone and palatine bones are here. Then inferior nasal conca, it's a separate bone in the lateral wall of the nose. Okay? So, all these are the components of the skull, which we should be aware of. Now, let's see the joint formed by the skull. In skull, all bones are united by fibrous joint. Fibrous joint is a type of solid joint. And those are upper twist sutures. Okay? Except one joint, that is temporal mandibular joint, which is a synovial variety of joint. Okay? So, almost all bones are united by fibrous joint, which are upper twist suture, except one joint, which is synovial, that is the temporal mandibular joint. If you see the bones of the ossicles, those are also synovial. Those are not included in joints of the skull. Okay? That has to be considered separately. Let's see the difference between an adult skull and a fetal skull. So, here we can say this is the adult skull viewed from the anterior aspect. This is the fetal skull viewed from the anterior aspect. The one most striking difference which we can see between these two skulls is, see the proportion of the facial skeleton here and see the proportion of facial skeleton here. Okay? Facial skeleton is very less developed in a fetal skull. The cranial skeleton is more developed because of the growth of the brain. Okay? So, facial skeleton is very small in a fetal skull and facial skeleton is well developed in an adult skull when viewed from the anterior aspect. And here we can see this region is the region of fontanel. This is the anterior fontanel of the skull. Fontanels are replaced by sutures in adult skull. So, in the skull here there will be a coronal suture, a sagittal suture which will be meeting at a point that is referred to as bregma. Okay? And here we can see a suture which is connecting the two frontal bones. If it persists in adult, it is referred to as metopic suture. Okay? Most of the time it is fused. And when seen from the lateral aspect, there is one important feature which is seen on the lateral aspect. This is the mastoid process. Okay? Mastoid process is seen well developed in an adult skull. It is not developed in the fetal skull. Okay? It develops due to the pull of the sternocleidomastoid muscle. It starts developing at the age of two years. Okay? So, these are some differences between an adult skull and fetal skull. And fontanels, if we see there are six fontanels. One is the anterior fontanel, one is the posterior fontanel, then anterolateral, posterior lateral on each side. Okay? So, all these fontanels will be fused in an adult skull. So, let's summarize what we have covered in this session. We started with the introduction of the skull. We saw what is the difference between skull and cranium. Skull without mandible is considered as cranium. Okay? In anatomical position of the skull we saw, the skull has to be held in anatomical position in such a way that the inferior margin of the orbit and the superior margin of the external acoustic maya test should lie in one horizontal plane. That line is referred to as Frankfurt's plane. Okay? In parts of the skull we saw there is a cranial skeleton and facial skeleton. We saw various bones forming the cranial skeleton, various bones forming the facial skeleton. Then in joints, almost all bones are united by sutures except one joint that is temporal mandibular joint, that is the sinoval joint. Okay? Whereas other bones, whereas other joints are the fibrous joints. Okay? And we saw differences between the adult skull and fetal skull. Okay? So, this was just an introductory lecture of the skull. In subsequent sessions, I will be covering the various parts of the skull, the exterior of the skull, the interior of the skull, the other various headings in which the exterior of the skull is studied. Norma verticalis, Norma occipitalis, frontalis, lateralis, basalis. Okay? So, all these topics will be covering in the subsequent sessions. Okay? Thank you.